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The squash (Cucurbita maxima) is a coarse, annual plant grown in practically all parts of the United States. It has long, running, cylindrical stems which are somewhat prickly and hairy. The stems are often 12 to 24 feet in length and root freely at the nodes. They are nearly always grown from seed planted in the field and only rarely started under protection and transplanted.
Seed of the Golden Hubbard variety was planted June 2, in hills 8 feet apart, at the rate of three seeds per hill.
Early Development.--When examined on July 13 the plants had each about 12 large green leaves, of which the blades were 3 by 5 inches in width and length, respectively, and 7 smaller ones. In addition there were 4 or 5 discolored and dead leaves. The plants were 8 inches high and had a total spread of 1 foot. The leaf surface was 3.4 square feet.
The root system was characterized by a strong taproot which, although zigzagging considerably in the hard soil, pursued a rather vertically downward course. Maximum depths of 28 to 32 inches were attained. The upper portion of the taproot was quite fleshy. It was 7 millimeters thick near the ground line but tapered to a width of about 1 millimeter at a depth of 7 inches. At greater depths it became quite thread-like. Many long, mostly horizontal branches, the longest extending 30 inches laterally, and numerous short ones arose from the first 18 inches of the taproot (Fig. 87). At greater depths the laterals were short and simple. The last 2 to 3 inches were without branches. In the surface 18 inches laterals occurred at the rate of five per inch, approximately two-thirds of them having a length less than 1 inch. Most of these short roots were unbranched, some were poorly clothed with branches. But on the longer branches laterals occurred rather regularly at the rate of five to eight per inch and varied in length mostly from 0.1 to 1.5 inches. Some of the laterals on the older roots were again branched and the rather infrequent, long, secondary branches were well furnished with rootlets. Thus the plant was rapidly developing a widely spreading and efficient absorbing system.
Fig. 87.--Golden Hubbard squash 6 weeks old. Note especially the widely spreading, shallow roots.
As a whole the root system was slightly yellow in color; many of the smaller laterals were quite yellow but the younger portions were always glistening white.
Midsummer Growth.--Two weeks later a second examination was made, July 27, when the plants had just started to blossom. The plant finally selected for detailed study had a total length of 6.5 feet. The main stem had two branches and a total of 20 large leaves and 8 smaller ones. Some of the largest plants possessed twice this number of leaves. A very large transpiring area was presented by these leaves, since those of larger size had blades averaging 9 by 8 inches in length and breadth, and the smaller ones 4 by 4 inches, respectively. The plants were making a very vigorous growth.
The general root habit was of the same plan as that found 2 weeks earlier but much more extensive and elaborate. The taproot, which was now 1 inch in diameter near the soil surface, penetrated downward in a very zigzag manner, tapering to 2.5 millimeters at a depth of 6 inches. At greater depths its diameter was variable, decreasing to 1 millimeter but enlarging again to 2.5 millimeters only to become more slender at deeper levels. Near the root end, at 42 inches depth, it was 2 millimeters thick. Not only had the root thus increased I foot in depth but also the former maximum lateral spread of 30 inches was now extended to 5 feet. This was attained in the surface 8 inches of soil. In fact, the chief growth was that of the laterals which had extended more widely, were more profusely branched, and had many more longer branches than before. The degree of ultimate branching had also increased. In regard to root habit in the deeper soil, i.e., below 19 inches, it was almost identical with that in the second foot of soil at the earlier examination (Fig. 87). A few of the deeper roots were decayed.
Maturing Plants.--A final study was made Aug. 21. As usual several plants were examined but the one chosen for final study had two main vines. One of these was 18 feet long and had five branches which were 3 to 7 feet in length. The other was 21 feet in length with seven branches, the longest being 7 feet. These vines were furnished with two rows of leaves. The leaves averaged 1 foot in length and width. Thus they presented an enormous transpiring area, probably losing several gallons of water in a single day. The plants were in the late blossoming stage. Nine fruits ranging from 2 to 7 inches in diameter were found.
The squash plant in its later development is very much like certain native plants in having two rather distinct parts to its root system. The one is largely superficial but widely spreading and the other spreads much less in the deeper soil where it may reach depths of 6 to 7 feet.
The taproot and its deeper branches had made considerable growth and were extensively branched to the 6-foot level. The branches were, however, relatively short so that below 2 feet not a very large volume of soil was occupied. Some of these deeper roots were decayed at the tips.
The most important, most active, and by far the most extensive portion of the root system occupied the surface soil. Five to seven main shallow roots were common. These were 4 to 7 millimeters in diameter and, although 10 to 14 feet long, usually ran at a depth of only 6 to 8 inches below the soil surface and were never found below the 12-inch soil level. Even near their tips and after giving rise to numerous large branches, they were still 2.5 millimeters thick. As shown in Fig. 88, they spread on all sides of the plant and branched profusely except in the first 12 to 18 inches of their course in which branching was sparse.
Fig. 88.--View of the root system of squash after the removal of the surface 12 inches of soil. The roots were excavated on Aug. 21 when the plant was about 11 weeks old and the main roots were still growing at the rate of nearly 2.5 inches per day.
In studying the figure it should be kept in mind that all of the main roots were between depths of 4 and 12 inches and usually at the 6- to 8-inch level. Sometimes they turned upward or downward abruptly (in which case they usually gave rise to major branches) but often ran for several feet at approximately the same depths. These shining white, cord-like structures penetrating the mellow soil, the last 8 inches or more usually being free from both root hairs and branches, were striking objects in the dark-colored soil. Frequently one could pull out five or more inches of root ends intact.
The numerous main lateral branches on these widely spreading roots greatly increased the general root territory which later the sublaterals with their branchlets so thoroughly occupied. Most of these roots had extended 12 feet and some to a distance of 17 feet from the hill. Because of their curved and tortuous courses the lateral extent was usually much less than the actual root length. Branches occurred at the rate of about four to five per inch. For the sake of clearness only a part of the branches have been included in the drawing. Most of them were 4 to 14 inches long and well rebranched. Infrequently, long branches (1 to 2 per foot of root) occurred. They varied from 2 to 8 feet in length and were rebranched profusely. Practically all were found in the surface foot, sometimes very near the soil surface. A few penetrated into the deeper soil but only rarely did they occur below the 2-foot level. The roots were white and tough and rather readily excavated.
Determination of the Rate of Growth.--To determine how rapidly the roots were growing, the following experiment was performed. The soil, 10 to 15 feet from the hill, was carefully examined until the uninjured, glistening white, smooth ends of the main roots were found. The end of the root was immediately engaged in a loop of stout cord and the root quickly covered with moist soil. The cord was tied to a small stake driven by the side of the root, the upper end of the stake being plainly visible and marking the position of the root when the soil was entirely replaced. Several roots were marked in this manner on Aug. 22. A week later an examination showed that some of the roots had made a growth of 17 inches in length, nearly 2.5 inches per day. Great changes, moreover, had occurred. The marked, unbranched root ends were now clothed with branches 0.3 to 2 inches long. The diameter of the root had decreased to one-half or only one-third of its former size. Microscopic examination showed that this was due to a shriveling of the deteriorated cortex. Root tips showed the beginnings (primordia) of lateral roots to very near the growing point. These had grown through the cortex and elongated 2 inches and the cortex deteriorated in the moist soil all during a period of 7 days. During a 2 weeks period some of the roots elongated 2 feet . It is evident that the picture (Fig. 88) is incomplete. A mature root system fills the soil to a distance of 15 feet on all sides of the plant. Seven hundred cubic feet of the richest soil may be occupied by the roots of a single plant. How thoroughly the soil must be ramified in a field of corn where squash or pumpkins are growing among the corn! There must be keen competition for water and nutrients unless the corn at this season is depending more largely on the deeper soil for its supplies of these essentials.
Still another part of the root system is to be described but just how important it became was not ascertained. The squash plant takes root at most of the nodes of the prostrate stems. At this time these roots were just beginning to develop. They were found to penetrate 4 to 8 inches deep and then turn and run laterally, often again approaching the soil surface. The shaded and protected vine-covered soil dries slowly and long, thread-like, minutely branched laterals were found just beneath the soil surface. These were already often 2 feet long (Fig. 89).
Fig. 89.--A typical root originating from the node of a squash vine. It is only partially developed.
Summary.--The rooting habit of the Hubbard squash is very similar in general plan to that of the watermelon and other cucurbits. The deeper portion of the taproot system is better developed, however, and the shallower part almost as extensive as the coarse, widely spreading vines. Plants with a spread of tops of only a foot are rooted 2.5 feet deep and are supplied with numerous, much branched, horizontal laterals 16 to 30 inches in length. Thus an efficient absorbing system is developed early. Within a period of 2 weeks and when blossoming has just begun, the vines have grown to a length of 6.5 feet. The taproots have increased only a foot in length but the horizontal laterals 2.5 feet, thus spreading somewhat less widely than the vines. Branching throughout is much more profuse.
Maturing plants have a wonderfully intricate and extensive root system which still develops at the rate of approximately 2.5 inches per day. A plant with stems 18 and 21 feet long has a taproot which is extensively branched (but with short laterals only, below 2 feet) and reaches the 6-foot level. Branches spread rather widely in the second foot but are relatively of less importance than the really wonderful root development in the surface foot of soil. A radial spread of 13 to 19 feet is attained. Five to seven main roots, with numerous branches 2 to 8 feet long and all again rebranched, form the groundwork which supports a remarkably branched root network that completely ramifies the surface foot of soil. Nodal roots, already 4 to 5 feet long and also superficial but extremely well rebranched, increase the absorbing area. Thus nearly 1,000 cubic feet of soil give of its supplies of water and nutrients to the support of a single plant.
Other Investigations on Squash.--Descriptions and measurements made on a squash plant grown in Massachusetts are of interest since they have been widely quoted and much disputed.
But our squash vine affords the most astonishing demonstration of all that has been said about root development. Growing under the most favorable circumstances, the roots attained a number and an aggregate length almost incredible. The primary root from the seed, after penetrating the earth about 4 inches, terminated abruptly and threw out adventitious branches in all directions. In order to obtain an accurate knowledge of their development, the entire bed occupied by them was saturated with water, and, after 15 hours, numerous holes were bored through the plank bottom, and the earth thus washed away. After many hours of most patient labor, the entire system of roots was cleaned and spread out upon the floor of a large room, where they were carefully measured. The main branches extended from 12 to 15 feet, and their total length, including branches, was more than 2,000 feet. At every node, or joint, of the vine, was also produced a root. One of these nodal roots was washed out and found to be 4 feet long, and to have 480 branches, averaging, with their branchlets, a length of 30 inches, making a total of more than 1,200 feet. As there were 70 nodal roots, there must have been more than 15 miles in length on the entire vine. There were certainly more than 80,000 feet; and of these, 50,000 feet must have been produced at the rate of 1,000 feet or more per day. 26
The vine grew at a maximum rate of 9 inches per day. The total extent of the main vine was 52 feet. the lateral branches being removed when 2 to 3 feet long. It had 100 leaves. The largest leaves were nearly circular and slightly lobed. Their diameter was 2.5 feet and the area about 700 square inches. 26
This remarkable root development has been quoted widely in many of the older standard textbooks of botany and plant physiology but later its authenticity was questioned. 52 This led to a similar experiment in England with a gourd plant (Cucumis sativus). The gourd was grown in a frame 10 by 6 feet in dimensions under the most favorable conditions. The roots were examined when the plant was fully grown and had borne 14 fruits. The vine with its branches measured 32 feet long and bore 140 leaves. The roots were recovered by so carefully washing away the soil that none were lost. Careful measurements of both the main root system and the nodal roots gave a total length of 281 feet. 52 The small size of the gourd root as compared with that reported for the squash has led some facetious reviewer to remark that the "figure [for the squash] is exaggerated and applies perhaps to Jonah's gourd but not to any other cucurbit." 39
A careful comparison, however, as regards number and length of main roots with that of the squash plant already described leads one to more nearly accept the Massachusetts findings. It is unfortunate that the work was not accurately checked. At least it has served a purpose in calling attention to the remarkable extent to which the root systems of cucurbits may develop. Of course, length in itself is not of such great significance as absorbing area. Many of the larger and older roots rapidly lose the power of absorption and serve only for conduction. It may be recalled that root decortication, in the field experiment where the rate of growth and branching was determined, occurred within a week after the new root growth.
Mature squash plants were examined at Geneva, N. Y., where they had grown in a fertile clay loam soil underlaid at a depth of 6 to 10 inches with a tenacious subsoil of gravelly clay.
The roots of this vegetable were examined with considerable interest, because it has been often stated that they extend as far as the runners. Observations showed that this view is based upon fact; indeed, in the bush varieties, the roots extended much further than the stems. In a plant of the Yellow Scallop Bush squash, examined Sept. 8, a root was traced horizontally a distance of 8.5 feet without reaching the end, while the longest runners extended but about 4 feet. This long root grew almost its whole length within 3 inches of the surface. In a plant of the Hubbard squash, of which the roots were washed out Sept. 11, one of them was traced horizontally a distance of 10 feet from the base, and at this point it was 1/8 inch in diameter, or about a third of its thickness at the start. It might doubtless have been followed much further, but was accidentally broken at this point and the remainder could not be distinguished among many other roots. This long root grew at a depth of 2 to 5 inches below the surface. It frequently changed its course, but pursued in general a rather straight line. It put out branches throughout its length, some of which were 1/8 inch in diameter. The number of branches in the 10 feet was 385 or on the average 38.5 per foot. 44
At Saratov, Russia, it was found that the chief mass of the roots of squash occurs in a soil layer not more than 12 to 16 inches deep. The main root had a diameter of 28 millimeters before it began branching at a depth of 2 inches. Beyond 2 inches it tapered gradually to 1 millimeter in thickness at a depth of 39 inches. The soil at this depth was very hard, the root was broken and not traced farther. Below a depth of 16 inches there was very little branching. The largest and longest laterals were found at a depth of approximately 2 to 5 inches in the mellow surface soil layer.. The strong horizontal roots spread to distances equal to that of the vines which were 11.5 to 20.3 feet long. The ends of the roots were less than 1 millimeter thick. Some laterals of the second and third order reached a length of nearly 16 feet. With their profuse branches they formed a dense network in the surface soil. The root system was found to be less extensive than that of the watermelon and citron but exceeded that of the muskmelon and cucumber. 76 Other investigations confirmed this study. In the black soil of Russia a great development of horizontal roots occurred in the plowed horizon, comparatively few roots of the second order penetrated vertically to a depth of about 40 inches. 76a
These studies all agree in confirming the extensive and superficial rooting habits of the squash and the lesser development of the more deeply penetrating portions.
Root Development in Relation to Cultural Practice.--Both the root and aboveground habits of squash are so similar to the cucurbits already described that it is not surprising that soil preparation, methods of planting, fertilizing, cultivation, etc. are very similar to those already discussed. The chief difference is that the squash is a somewhat hardier plant, does not require so long a growing season, and is not so exacting in its requirements.
In applying barnyard or other coarse manures to the soil, especially where relatively shallow-rooted crops like the cucurbits are grown, it should be the prime object to mix the manure with the soil as thoroughly as possible. If it is turned under in thick layers, without being disintegrated and mixed with the soil to a considerable extent, the layer of manure will prevent the capillary moisture from reaching the upper layer of soil and thus cause the plants to suffer for water very soon during drought. Under such conditions roots have been repeatedly observed to make a vigorous growth in the enriched layer and branch profusely. But when this poorly compacted layer becomes dry the absorbing rootlets die and the main roots merely serve as conductors between the rootlets still functioning in the moist layers below and the parts aboveground. Hence, well-decomposed stable manure is best for the garden, especially when manure is used in large quantities. It is easily mixed with the soil which becomes compacted about it. Thus not only the main roots of the plants but those arising adventitiously from the nodes find a congenial substratum for growth.
Roots of Cucurbits in Relation to Disease.--The development of nodal roots in squash and pumpkin is connected in a measure with recovery from the injuries of certain insect enemies. The squash vine borer in the larval stage of development tunnels into the stem at or near the soil surface. Usually decay sets in, water conduction is interrupted, and the vine begins to wilt. Covering the stems with soil so as to encourage the development of nodal root growth is a common control measure. Although preferring squash and pumpkins, the borer attacks all species of cucurbits, often causing great destruction.
Examples of other disease-producing organisms attacking or gaining entrance through the roots of cucurbits are as follows: Watermelon wilt is caused by species of Fusarium fungi which live in the soil and through the roots gain entrance to the water-conducting tissue of the stem. When, due to the growth of the fungus, the water supply becomes insufficient the vines suddenly wilt and die. Root knot, due to a nematode, causes the roots of watermelons to become greatly enlarged, the vines to lack vigor, and the melons to remain small. The striped cucumber beetle tunnels in the main roots or stems of various cucurbits below ground. Blossom-end rot is probably a physiological trouble of watermelon brought on by rapid changes in soil moisture just as the young fruits are starting to grow. 146
As pointed out elsewhere, the relation of root development to disease resistance of crops is important and requires intensive study. Recent experiments have demonstrated a close relationship between root growth and disease resistance. 59A thorough knowledge of the development of the root habits of cultivated crops is needed in combating plant disease produced by soil-borne parasites or resulting from physiological-environmental relations of the root systems.