372 ANNUAL, REPORT OF THE Off. Doc. 



The alder is therefore the one non-leguminous plant which is able to 

 assimilate atmospheric nitrogen. 



Regarding other non-leguminous plants, the question of nitrogen 

 nssimilation has been raised, but the answer has, on the best author- 

 ity, been in the negative. Thus Lotsy^^ showed the inability of white 

 mustard to utilize free nitrogen and the same was shown by Nobbe 

 and Hiltner^" regarding mustard and buckwheat. 



So far as present knowledge goes we may, therefore, assume that 

 plants without tubercles are unable to utilize free atmospheric 

 nitrogen. 



4. Are There Different Species of Root Tubercle Organisms. 



This is a question which has frequently been raised, but which as 

 yet cannot be positively answered. 



Nobbe held that there is a separate race of bacteria for each species 

 or group of nearly allied species of plants. On the other hand Maz6, 

 an equally good authority, claims that there are certain physiological 

 forms of bacteria determined by the nature of the media in which 

 they are developed. These are able to inoculate the roots of plants 

 growing in soils offering the proper conditions for their develop- 

 ment. 



Beyerinck^^ has made a careful study of the different forms of 

 bacteroids found in different species of legumes, and records dif- 

 ferences among them. Voelcker^^ illustrates 16 different forms of 

 bacteroids from different species of legumes, but states that no cul- 

 tivating these organisms on nutrient juedia their differences disap- 

 pear and that they can no longer be distinguished the one from the 

 other. 



This would indicate that differences in the form of the organism, 

 as seen witlhin the plant, has little significance, and is controlled per- 

 haps entirely by the differences in the host. For it is a well known 

 fact that one and the same bacterial organism will often present 

 variations in form when grown in media of different character. 



It is thus evident that the question of differences of species can- 

 not be settled from the standpoint of differences of form, but must 

 be determined from the physiological side. 



Nobbe, Hiltner and Schmid^^ have thrown important light on the 

 question in their inoculations of different legumes with pure cul- 

 tures. 



Their experiments show that the organism from a single species of 

 legumes is capable to a greater or less degree of infecting and of 

 producing tubercles on the roots of a number of distinct species. 

 Thus the vetch can be infected by means of culture from Robinia 

 (locust) Acacia, Vicia (vetch), and Pisum (pea); but the greatest de- 



