30 Development and Activities of Roots of Crop Plants. 



A comparison of these results with those obtained at Peru shows a much 

 more extensive root development at the latter station. At the New York 

 Experiment Station only was the lateral spread as great, while in no case 

 was the depth of penetration so pronounced. These dilBferences may be due 

 in part to the variety of potato grown, and to variations in environmental 

 conditions both cUmatic and edaphic. It seems, however, that, at least in 

 some cases, the method of excavation was faulty, in that the entire root 

 system was not recovered. In most cases the roots were washed out, and 

 the fragile younger and finer parts largely destroyed. In some instances, 

 too, it seems clear that the block of earth prepared for washing was not 

 extensive enough to include all of the roots. 



Comparison of Root Systems. 



The most obvious conclusion from a consideration of the data is that these 

 crop plants, Uke the prairie species that preceded them, are provided with 

 well-developed, deep-seated, and extensive root system (cf. Weaver, 1919, 

 1920). All of the cereal crops examined are similar in having two more or 

 less distinct parts of the root system as regards position. One group of 

 roots in each case spread out horizontally in all directions from the base of 

 the plant and had for its main function absorption from the shallower stratum 

 of soil. In most instances these lay within a foot of the soil surface. The 

 other group of roots, which completed the underground part of each plant, 

 pursued a more or less vertically downward course and penetrated deeply. 

 The potato also had a shallower and a deeper portion of its root system. How- 

 ever, in the development of the potato this end is accomplished in a different 

 manner. Instead of having two more or less different groups of roots, as 

 in the cereals, the same group served both purposes. This was brought about 

 by developing at first a copiously branched, shallow, horizontal group of 

 roots. Later, by turning rather abruptly downward and continuing their 

 course into the subsoil, these also became the deeply penetrating ones. In time 

 of development of these two portions of the absorbing system, the plants 

 fall naturally into two groups ; the small cereals forming one group, and corn 

 and potatoes comprising the other. In the former group both the shallow 

 and the deeper penetrating portions began to form more or less simultaneously 

 in the earUer stages of growth. In the latter the shallow system had devel- 

 oped to a rather marked degree before the deeper penetration of the soil 

 began. However, both groups agreed fairly well in that the shallow roots 

 had practically reached the Umit of their horizontal spread by the time the 

 tops were in the intermediate stages of growth. Conversely, the longer 

 roots continued to penetrate deeper until the plants were almost if not indeed 

 entirely mature. 



All the root systems, as might be expected considering their fibrous char- 

 acter, were well supplied with small branches. But in this particular an 

 examination of the figures shows that the corn and potato were much more 

 abundantly furnished with branches than were any of the others. A com- 

 parison of the relative development of tops and roots shows the greater 

 extent of the underground parts in every case except that of corn. They 

 regularly penetrated to a depth at least twice as great as the height of the 

 tops. Indeed, in some instances, especially among the smaller cereals, the 



