78 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. lxii. 



These unicellular plants containing chlorophyll are quite 

 comparable with the single chlorophyll cells of compound 

 plants, and are so like them iu every way as to make it 

 very ditlicult to deny to them the power of assimilating 

 free nitrogen. 



But while that goes so far as to make it a reasonable 

 view, it does not explain why it is that the faculty of 

 absorbing free nitrogen should be possessed by the chloro- 

 phyll cells of the Leguminosa3 any more than by those of 

 any other order of chlorophyll-bearing plants. Frank has 

 endeavoured to throw some light on this by following up, 

 as far as possible, the fate and progress of the bacteroids 

 within the nodules aiid without. From a minute examina- 

 tion of the tissues of the root in the neighbourhood of the 

 nodules, he finds that these organisms make their escape 

 from the nodule in the root, and that they are to be found 

 there especially in the riper stages of its life. It is his 

 belief that long before the nodule softens and breaks down, 

 and is in great measure absorbed by the plant, it is passing 

 its bacteroids into the general circulation ; and he has been 

 able to detect these Y-shaped or forked organisms in the 

 cells of the stem, the leaves, the seed itself, and even in the 

 cotyledons of tlie young embryo of Fhascoliis vulgaris. The 

 identification of these minute organisms is attended with 

 great difilculty, and there is considerable liability to error ; 

 but Frank is very strong upon the point that he is not 

 mistaken in his search for these bodies, and if that is so, 

 if his observation is to be trusted, and if it is really certain 

 that the plant is permeated even very thinly with bacteroids, 

 it makes it more easy to believe that under their stimulus 

 the function of aljsorption of free nitrogen may be imparted 

 to the chloropliyll cells, in virtue of their presence in 

 some unknown way. It would, in that case, be more easy 

 to compare the chlorophyll cell of the Leguminosa.' with the 

 unicellular algic of the soil, for it is rpiite possible that 

 these also owe their power of assimilating free nitrogen to 

 a stimulus received from similar bacteria contained in the 

 soil. 



The finding of bacteroids in the cotyledons of Fhaseoh/s 

 vulr/arts is also a matter of great- interest, for if that is 

 correct, and if the case is not an isolated one, it is evident 



