ROOT DEVELOPMENT OF CROP-PLANT ECADS. 131 



series of experiments carried on under conditions where the effect of each 

 factor can be evaluated. 



In this connection, the results of certain other investigations are of interest. 

 Headden (1896) excavated alfalfa roots in three different counties in Colorado 

 in soil varying from sandy loam to heavy clay. He stated : 



"They show a marked permanency in type of development in a simple tap- 

 root, running down from 3 to 5 feet and then sending off a few side roots, or 

 rather dividing into a few branch roots of about equal size and length. These 

 branches do not as a rule deviate more than a few inches from the course pur- 

 sued by the tap-root before division. I have in no case found a system of 

 small roots starting out below and near the crown, extending laterally for 

 several feet and then turning downward. The tap-root is often perfectly 

 smooth, save for wart-like excrescences on it caused by symbiotic micro- 

 organisms." 



Six-year old plants on stiff clay soil near Fort Collins were found to pene- 

 trate to a depth of 11.8 feet in one instance and to 12.3 feet in another. In 

 speaking of the effect of age on roots he states: "I have seen many roots of 

 6-year-old plants smaller than roots of other plants which we knew to be only 

 9 months old." He also says that 7 feet is as deep as a large percentage of 

 alfalfa plants penetrate in our soils. He cites cases of yearling plants penetra- 

 ting to a maximum depth of 3.8 feet in fine prairie loam, while a 9-months-old 

 plant was found with a root-length of 9.4 feet. "These differences in develop- 

 ment of roots are no greater than I have often found and I see no satisfactory 

 explanation for facts." 



Cottrell (1902) has followed the tap-roots of 8-year-old alfalfa in stiff "hard- 

 pan" soils in Kansas to a depth of 10 feet without finding an end. "The roots 

 extend 15 to 30 feet and more in depth in fairly good soil." 



Ten Eyck (1904) excavated 3-year-old alfalfa roots on an upland loam at 

 Manhattan, Kansas. Several roots were traced to a depth of 8.5 feet. 



Sweet clover (Melilotus alba). — An examination of the development of the 

 roots of sweet clover was made on June 13, when the plants were 49 days old. 

 The crop in both areas was growing very well, but the plants in the upper plats 

 were only 3 inches in average height as compared with a height of 10 inches for 

 those in the valley soil. The pronounced development of the tap-root may be 

 seen in plate 17, b, which shows two typical specimens from each site. The 

 main roots pursued an almost vertically downward course ; those in the upland 

 reached a working depth of 1.3 feet, and those on lowland soil 1.8 feet. The 

 maximum depth of root penetration attained on the two sites were 1.3 and 2.6 

 feet, respectively. The roots were exceedingly well branched throughout 

 their course, even to their tips. The branches were small and mostly 2 inches 

 or less in length, although some had reached a length of 5 or 6 inches. Of the 

 numerous plants examined, the light-colored tap-roots had a diameter of only 

 1 to 3 mm. 



On August 18 the roots were again examined. The plants in the upper plats 

 were 1.5 feet in average height and in excellent condition, some of the tallest 

 reaching a height of 2 feet. Those growing in the lower plats were likewise 

 in a flourishing condition, with an average height of 1.8 feet and a stem diam- 

 eter of 5 or 6 mm. The root development of a typical specimen from the lower 

 plat is shown in figure 36. The tap-roots here were seldom over 6 mm. thick 

 and usually only 4 or 5. They pursued a more or less vertically downward 

 course, the tap-root tapering rapidly. The deeper roots of many plants 

 reached the 5-foot working level, but few penetrated beyond, and these for a 

 distance of only 0.2 to 0.3 foot in the moist soil. The main roots were only 



