268 FIXATION OF FREE NITROGEN BY BACTERIA 



up, in older layers (v), the commencement of branching is already discernible? 

 and is found in a more forward state in a still higher position (x). Finally, in 

 a section across the cells of the fnternal tissue of the nodule in the direction y 

 (Fig. 60), none but variously shaped bacteroids (y} for the most part united to 

 form reticulated bands (shown in Fig. 64) occur. After attaining this condition 

 the bacteroids are soon dissolved by the surrounding cell plasma and disappear. 

 However, before this occurs, small globular vesicles of an unknown nature, which, 

 however, should not be regarded as endospores, not infrequently appear in the 

 interior of this formation. Little can as yet be said of the chemical composition 

 of the contents of these bacteroids. Micro-chemical reactions, however, indicate 

 that the greater part is composed of albumen. Certain enclosures are also 

 frequently observed, A. B. FRANK (VII.), for instance, having noticed such 

 bodies in the bacteroids of individual nodules of peas. He regarded them as 

 amylodextrin, the discovery leading him to the opinion that two kinds of nodules 

 develop on these Papilionacece : albumen nodules and amylodextrin nodules. A 

 subsequent investigation of this matter by H. MOLLER (I.) showed, however, 

 that these doubtful enclosures do not consist of carbohydrates, but of waxy 

 or fatty substances; that they are also to be found in the bacteroids of the 

 " albumen nodules " ; and that, moreover, there is but little probability of the 

 existence of dimorphism in the root-nodules of the pea, since these enclosures 

 are also occasionally met with in the bacteroids of the nodules of other Legu- 

 minosce (e.g. Trifoliunt repens). 



Concurrently with the reproduction and transformation of the bacteria 

 marches the development of the nodule, which not only increases in size, but 

 also becomes richer in nitrogenous compounds. This gradual increase in the 

 percentage of combined nitrogen in the nodules and the relative proportion of 

 this substance there present, as compared with other parts of the root, were 

 quantitatively investigated by J. STOKLASA (II.). From his results a few 

 figures have been collected into the subjoined tables, which refer to yellow 

 lupins : 



That this nitrogen of the nodules was chiefly in the form of albumen is 

 revealed by the following table : 



The figures just given are surpassed in two analyses made by A. B. Frank, 

 according to which a few of the pea nodules examined by him contained 6.94 per 

 cent., and those from the dwarf bean 7.44 per cent, of nitrogen, corresponding 



