12 



BULLETIX 1087, U. S. DEPAETMEXT OF AGRICULTURE. 



into consideration. In order to obtain a more tliorough conception 

 of its effect data were obtained on the extent of the mortality be- 

 tween 1917 and 1919, measurements being also made showing the 

 increase in root diameter during this period. The data obtained 

 showed rather conclusively that the dying of the plants in the field 

 resulted in a larger taproot growth of the survivors and that the 

 roots of the plants surviving were of a more branching type. A 

 decrease in the stands of the less hardy alfalfas, during a growth of 

 four seasons, amounted to as much as 22.5 per cent and was found 

 to be accompanied by an increase in root diameter of 74.9 per cent. 



Fig. 7. — Root .systems of plants of southern-grown common alfalfa (lledicago xativa), 

 indicating the large percentage of mortality occurring in this strain during the 6-year 

 period from Ifilo to 1920, inclusive. Roots marked X represent dead plants. 



while with hardy alfalfas where there was almost no mortalitj' the 

 increase was appreciably less. This amounted to 64.2 per cent in 

 Turkestan alfalfa and to 55.8 per cent in the Grimm variety. As 

 data which will be presented later show no distinguishing differ- 

 ences between these varieties and strains in the size of the taproot, 

 it is apparent that the greater increase in root diameter of the non- 

 hardy alfalfa was probably due to the thinning of the stands, which 

 not only eliminated the small plants but permitted a greater root 

 growth of the surviving plants. (Figs. 7, 8, and 9.) 



CHARACTERISTIC ROOT SYSTEMS OF SOME OF THE WELL- 

 KNOWN VARIETIES OF ALFALFA. 



An attempt is here made to describe and compare in a simple way 

 and to illustrate with photographs the types of root systems that 

 are characteristic of the best-known varieties of alfalfa. By so 

 doing it is hoped to convey a better idea of their points of similarity 

 and their differences than now appears to prevail. 



