No. 6. DEPARTMENT OP AGRICULTURE. 37i 



grown on a soil for the first time. Tlie roots of the plants growing 

 upon old ground were well supplied with tubercles, while in the 

 new soil thej were usually almost entirely absent. 



Lane,^^ in New Jersey, obtained similar results with the cowpea, 

 when grown for three successive crops on the same land. The first 

 season but few tubercles were noted, and the yield was 6.56 tons per 

 acre. The second year the tubercles were more abundant and the 

 yield was 7.19 tons per acre. The third season the tubercles grew 

 abundantly and the yield per acre was 10.02 tons. 



The fertilizer applied the third season was less than one-half 

 that applied the second and it is believed that the increase was due in 

 a large measure to a greater abundance of tubercles. 



It is a general observation that both annual and perennial legu- 

 mes grow better a secood season than they do the first, and this is 

 probably due to a larger seeding of the soil with the organisms nec- 

 essary to the production of tubercles on the roots. 



It is claimed by Nobbe and others that root tubercles exert no 

 influence in nitrogen assimilation when there is an abundance of 

 available nitrogen in the soil. The tubercles being held to be the 

 organs for such assimilation, this amounts only to saying that 

 these organs will not perform this function unless called upon to do 

 so, but let this necessity be forced upon the plant, the function of 

 the tubercles is exercised, and the greater their number the greater 

 will be the gain of the plant in nitrogen. 



Furthermore, the poorer the soil in available nitrogen, as shown 

 by Hiltner^^ in the case of Alnus glutinosa, the greater is the num- 

 ber of root tubercles which will develop, provided the necessary 

 organisms are present in the soil. Hence under conditions of nitro- 

 gen starvation or deficiency the number of tubercles on the roots 

 becomes a measure of the nitrogen assimilating activities of the 

 plant. 



3. Do Other Plants Than Legumes Assimilate Free Nitrogen? 



The power of legumes to assimilate free nitrogen does not rest 

 on the fact that they belong to a certain family of plants, the Legumi- 

 nosae, but rather to the fact that their roots contain tubercles. 

 Thi? is instanced by the common alder whose roots bear tubercles. 

 Hiltner has shown that young alders without root tubercles, and 

 deprived of combined nitrogen, are unable to assimilate atmos- 

 pheric nitrogen, and that the plants are poorly developed. But when 

 by inoculation, tubercles are produced, the plant can utilize free 

 nitrogen as in the case of legumes. This is well illustrated in Fig. 9. 



