64 



Miss M. Dawson. 



B. Experimental Work. 



a. Pure cultures of the organisms from Fisum, Besmodium, and 

 " Nitragin," upon various media, liquid and solid, organic and inorganic, 

 employing the ordinary methods of bacteriology. 



13. Direct observations under the microscope of the various stages of 

 growth of colonies, and the formation of bacteroids from straight rods, 

 as seen in hanging drops. 



7. Experiments upon the effect of temperatures above the normal 

 upon the direct infection of pea roots. 



8. Cultures of various genera, representing different tribes of the 

 order, to test the power of organisms proper to one genus to induce 

 tubercle formation upon individuals of other genera or tribes. 



€. Crop cultures in the laboratory greenhouse of peas in sterilised 

 media, with and without inoculation with " nitragin," also with and 

 without a supply of nitrogenous food. 



(. Crop cultures of peas in ordinary garden soils and in subsoils, in 

 the open, with and without inoculation with "nitragin," also with 

 and without an additional supply of nitrates. 



A further study of the morphology of nodules from various genera 

 of the Leguminosese, leads to the conclusion that no definite line of dis- 

 tinction can be drawn between genera in which filaments occur in the 

 nodules and those in which they have not yet been observed. Several 

 examples were found of fragmentary portions of filaments in the cells 

 of very young nodules, whilst in older specimens these filaments were 

 quite absent {e.g., Fhaseolus, Desmodium, Acacia, and others), suggesting 

 an intermediate stage in the adaptation of the parasite to the special 

 conditions existing in any given host. 



During the course of this study, some peculiar anatomical characters 

 have been observed in certain nodules, e.g., the presence of a definite 

 crystal layer in some genera, of apple-green nucleus-like bocKes in 

 Desmodium and Rohinia, and of organisms of an unusually large size 

 in Desmodium, Coronilla, Psoralea, and others. 



A prolonged study was made of the organisms from Desmodium. 

 gyrans in particular. Pure cultures were obtained, and from these 

 observations in hanging drops upon bacteroid formation showed that 

 the X and Y forms arise hy distinct lateral branching of the straight rods. 



After twelve to fourteen days' culture, the individual long rods tend 

 to break up into small rodlets, and the branched forms become dis- 

 jointed in a similar manner. A general study of these organisms 

 and parallel cultures of " nitragin," compared with pure cultures of 

 organisms obtained direct from Fisum tubercles, shows that they all 

 alike grow readily on gelatine or agar media containing an extract of 

 pea stems, asparagine, and sugar, but very slowly on broth gelatine. 

 They do not peptonise milk, but upon potato a watery streak is formed 



