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The pumpkin (Cucurbita pepo) is a species of the gourd family widely grown as a cultivated annual. Like the squash the most common varieties have long-running, prostrate vines, although the variety condensa or "bush-pumpkins" are neither running nor tendril bearing and the plants are more compact. 7 The pumpkin is grown in practically all portions of the United States but it is of much less commercial importance than the squash. In many parts of the United States pumpkins are frequently grown as a companion crop to corn.
The Small Sugar variety was planted June 2, in hills 8 feet apart, and at the rate of three plants per hill. The first examination was made three weeks later, June 24.
Early Growth.--The plants were scarcely 6 inches high but had a spread of 1 foot. The cotyledons were dead and dry but each plant had about three leaves, ranging from 2 to 3 inches in length and diameter, and a leaf surface of about 25 square inches. The stems at the soil surface were 5 to 6 millimeters in diameter but the taproot scarcely exceeded 2 millimeters.
The taproot tapered rapidly into a thread-like organ. About half of those examined pursued a rather devious course departing 2 to 6 inches from the vertical but all finally reached depths of 18 to 22 inches. The characteristic branching habit is shown in Fig. 90. Beginning scarcely 1 inch below the soil surface, lateral roots arose at the rate of 7 or 8 per inch to a depth of nearly 9 inches. Although many of these were short (6 inches or less), others pursued their horizontal or obliquely outward and downward course extending laterally 12 to 15 inches. A few extended outward and upward to within 2 inches of the soil surface. A maximum spread of 21 inches was found. All of these roots were branched at the rate usually of 6 to 12 rootlets per inch except the 2 to 3 inches of rapidly growing root ends. The branches varied from 0.2 to 1 inch in length. No tertiary rootlets were found. Below 9 inches the laterals were fewer, short, and unbranched. Thus most of the absorbing area at this time was distributed in the 6 to 9 inches of surface soil.
Fig. 90.--Small Sugar pumpkin 3 weeks old.
Midsummer Growth.--The second examination, July 24, showed marked growth both aboveground and underground. The main vines were over 7 feet long. The plant described had one large branch 5 feet long, originating near the base of the main stem, a second 16 inches distant was 30 inches in length, and a third 2 inches beyond, 32 inches long. There were also two short branches. The smaller branches had 10 to 13 leaves each, the larger ones 24, and the main stem 34. Thus a total of nearly 100 large leaves and 75 square feet of leaf surface were exposed to the hot, dry air of midsummer. The main vines were nearly I inch in diameter at their origin. Numerous large flowers further increased the transpiring area. A few small fruits were beginning to appear.
The root system had made a marked growth. The taproots were frequently over 0.5 inch in diameter but tapered rapidly to only 8 millimeters at the 6-inch level. In the deeper soil they were only I to 2 millimeters thick but the turgid, glistening white root ends again increased to a diameter of 4 millimeters. Depths of 4 feet were attained. Many of the taproots pursued a rather tortuous course. For example, at a depth of 1 foot they were sometimes 9 inches laterally from the base of the plant and throughout their course they were often much kinked and curved.
Most of the large laterals originated at depths of 2 to 10 inches. These strong roots were 3 to 6 millimeters in diameter. On plants of normal size frequently 10 main laterals arose from this portion of the taproot. These, in general, ran horizontally in the surface foot of soil and extended outward from 3 to 8 feet. For example, one large branch, originating at the 6-inch level, extended over 7 feet and at no time did it reach a depth greater than 8 inches. Thus the roots had spread as widely as the vines. Other roots ran laterally only 2 to 3 feet and then turning obliquely or quite horizontally downward often reached depths of 2 to nearly 3 feet. These branches sometimes forked rather dichotomously, frequently one of the branches turning downward and the other continuing its horizontal course.
All of the larger roots gave rise to long, vertically descending laterals which ramified the second and third foot of soil. As many as 12 of these long branches arose from a single root 6 feet in length which pursued its horizontal course between the 4- and 8-inch soil levels. These were clothed with an abundance of rootlets of the third order, in fact, so profusely that they formed dense networks at least to 6 inches on all sides of the parent root. Other branches on the main laterals arose at the rate of 5 to 10 per inch. They ranged from 0.5 to 2 inches in length but, frequently, branches 8 inches in length occurred. The longer branches were profusely rebranched, thus greatly increasing their absorbing area.
From the first 10 inches of the taproot, moreover, there arose frequently in small groups, short laterals seldom exceeding 4 inches in length, at the rate of three to four per inch. In fact the surface 12 inches of soil were so thoroughly occupied and absorption had been so great that they were very dry. A few of the root ends had dried out and died. But at greater depths moisture was abundant.
Below the 10-inch level the roots were relatively short; few exceeded 2 feet in length and the greater number were 8 inches or less. Their course was variable. Some ran horizontally, others almost vertically downward, still others ran outward and downward. The longer ones were so thoroughly rebranched that they formed glistening white, cobwebby mats in the darkcolored, moist soil. Branching from the taproot was somewhat irregular but at the average rate of 5 per inch. Only the longest branches were furnished with rootlets of, the third order and those of the second order below 3 feet were rare.
Thus the root system, as in the case of the squash, was differentiating into two parts, one thoroughly ramifying the surface soil, the other, less extensive one, occupying the deeper soil below the hill.
Maturing Plants.--A final examination was made Aug. 24. The plant examined was selected because of its average size and typical appearance. The main stem was 16 feet long. From near its base there arose two long branches; one 13 feet in length with a branch 10 feet long and another 14 feet in length with a single 4-foot branch. In addition, the main vine had three smaller branches 5 to 6 feet in length. The numerous large leaves presented an enormously extensive transpiring area. Many blossoms occurred and eight small fruits about 3 inches in diameter. In addition there were four larger ones 4 to 8 inches in diameter. As in the case of the squash, the root system was composed of two rather distinct parts.
The taproot system, or more strictly speaking its deeper portion, had reached a maximum depth of approximately 6 feet. Although ample rains had moistened the surface soil, the deeper soil was now quite dry and very hard. Depth of penetration (now 6 feet) had been increased about 2 feet over that of the previous examination. In general the branches were slightly more numerous, somewhat longer, and better rebranched. The, newer portion of the root was only poorly furnished with laterals. But some of the roots were withered and dry. It seemed that most of the energy of the plant had been used in developing the more superficial portion of the root system.
The extent of the surface root system had been greatly increased. Perhaps a description of a typical lateral will make clear the great extent and complexity of branching. A branch ¼ inch in diameter arose 4 inches below the soil surface. It ran outward 8 inches and branched somewhat dichotomously. Twenty inches from this fork one of the branches gave rise to a small root, only 1 millimeter in diameter, which ran 3 feet and ended in the surface soil. Eight inches farther a similar root arose. It extended vertically downward to a depth of 28 inches where the tip was dead. Eighteen inches farther on the branch a group of six laterals, 0.5 to 1.5 millimeters in diameter, originated. Three of these ran horizontally 22, 31, and 37 inches, respectively, occupying new territory in the shallow soil. Two descended almost vertically downward in parallel courses only about 8 inches apart to depths of 24 and 38 inches, respectively. The sixth ran obliquely outward and downward ending in a spangle of rootlets which had grown after the main branch had been destroyed. The main root, now at a depth of 1 inch, turned abruptly downward 1 inch, ran onward another inch, and then turned quite as abruptly back to its old level. Fourteen inches further, a large branch, equal to the main root in diameter, arose. This was followed 2.5 feet where it ended in the fifth inch of soil. The main root ended 12 feet from its place of origin. it was over 14 feet long, however, since it had not pursued a straight course but had curved and turned considerably. The other main branch was, in general, not unlike the one described.
Only the first foot of the root described was poorly furnished with small laterals. These were thread-like and only 3 to 4 inches long. Otherwise throughout its course it was branched at the rate of four to eight per inch. In addition to the. larger branches already described, many of the smaller ones, sometimes three per foot, were 1 millimeter in diameter and 2 to 4 feet long. The last 3 feet of the root was 2 millimeters thick, quite white in contrast with the yellowish color of the older parts, and furnished with rootlets 0.2 to 2.5 inches long. These were rebranched at the same rate, i.e., four to eight per inch, as the main root. Many of the hairlike branches of the surface root were 3 to 4 inches long and rebranched to the second order. Sometimes 15 branches per inch occurred. They ran in all directions, frequently upward to near the soil surface. The last 6 to 8 inches of main root ends were glistening white, unbranched, and growing rapidly.
This is a brief description of one-half of one of the laterals. Usually 6 to 10 such roots occurred, running in all directions from the base of the plant. Some were smaller (3 millimeters) and shorter, 5 to 8.5 feet. A few were longer and even more complex. A maximum spread of 17.5 feet was attained by one of the longest roots.
The great surface spread of these still rapidly growing roots should be visualized together with the dense network of roots they formed in the surface soil. In fact, the root system was much more branched than that of the squash. Attention should also be given to the deeper soil volume occupied by the vertically descending branches.
These branches arose in considerable abundance, even at distances of 6 feet from the base of the plant and sometimes were only 3 inches apart. Extending to depths of 24 to 38 inches and profusely branched and rebranched throughout, they added greatly to the volume of soil occupied. Many root ends, however, had decayed in the dry, hard soil below 3 feet.
Some of the larger branches, usually about 6 to 8, originating from the taproot at depths of 5 to 10 inches (rarely deeper) ran outward only 6 to 12 inches and then turned rather obliquely or nearly vertically downward. In some cases their course was obliquely downward from the beginning. These gave rise to branches both large and small but-none showed the horizontal tendency of growth so characteristic in the-surface soil. They usually penetrated deeply, anywhere from 30 to 45 inches. In the hardest soil layer, just above 18 inches, they were poorly branched, usually with 6 to 10 mostly simple branches per inch. These were not over 1 to 2 inches long. But below this level they were more thrifty and 6 to 8 abundantly rebranched laterals per inch of main root were usual. These were rebranched with 8 to 10 sublaterals per inch,, some of which were 1 inch long. Sometimes 15 branches per inch were found. It was evident that conditions for root growth in the deeper soil had been more favorable at an earlier period for now most of the roots below the 3-foot level were in an unhealthy condition.
The nodal roots were similar to those of squash. Usually the main root reached depths of 3 to 10 inches and then turned and ran horizontally 1 to 2 feet. They were densely rebranched. Often there were two or three roots originating at one node. Roots occurred at most of the nodes but not in such large numbers as were found on the squash.
Summary.--The Small Sugar pumpkin has a rooting habit somewhat similar to that of the Hubbard squash. Three-weeks-old plants have taproots which penetrate downward at the rate of 1 inch per day. Major branches occur only in the first 8 inches of soil. The longest extends horizontally nearly 2 feet. By midsummer the strongly branched vines are over 7 feet long and have 75 square feet of leaf surface. The rather crooked taproot has doubled in length. Below the surface foot the root network does not exceed 8 to 24 inches in lateral extent. But in the foot of surface soil the strong laterals, usually about 10 in number, spread outward 3 to 8 feet. Those of lesser spread often turn downward into the second and third foot and all give rise to vertically descending laterals, frequently in great abundance. Both main roots and their branches are so thoroughly furnished with rootlets that not only the surface soil but, to a lesser extent, the second and third foot as well are also fully occupied.
Maturing plants, with vines 16 feet in length, have taproots extending to the 6-foot level. The portion of the root system originating from the taproot below 12 inches makes relatively a small growth when compared with that in the shallower soil. The major surface laterals (usually 6 to 10 in number) are often ¼ inch thick and extend outward in rather devious courses 5 to 17.5 feet. Branched throughout their course at the rate of four to eight laterals per inch, many of which are 2 to 4 feet long and all complexly and minutely rebranched, they form a wonderfully efficient root complex. It is even more profuse than that of the squash and like it still grows rapidly. The obliquely penetrating roots extend into the fourth foot of soil. These and the very numerous vertical branches are features not found or at least not prominent in the squash. Descending into the second and third foot in great numbers and often at a distance of 6 feet from the base of the plant, laterals penetrating vertically downward thoroughly ramify the deeper soil. Nodal root development is similar to that of the squash.
The root habits and cultural requirements and practices are so similar to those of other cucurbits that they need not be further discussed.