(HARRISON et BARLOW] NODULE ORGANISM OF THE LEGUMINOSAE 169 



middle, often bent, more rarely branched. They are swiftly and actively 

 motile, darting, whirling and tumbling. In young colonies nearly all 

 the cells are motile, in older colonies fewer, and as long as the colony 

 continues to grow some motile cells may usually be seen. The cell con- 

 tents are not uniform, but denser protoplasm appears in plates and bands, 

 as in the branched cells direct from the nodule. This can be observed 

 in the living cells, but is best seen on staining. In this manner, several 

 surface colonies and as many deep colonies from each plate are isolated 

 and studied and the growth from each colony will be like that from 

 the others on the same media. Colonies developed in plate cultures 

 from pure cultures kept in stock as readily as from the nodules and 

 they are the same in appearance. 



The morphology of the bacteria taken directly from the nodules 

 varies with the species of legume, the conditions of infection and growth, 

 the age and size of the nodule, and the portion of the nodule examined. 

 These bacterial cells are so characteristic, so varied and so beautiful in 

 form as to be pleasing objects of study. In plants of the tribes Pliaseo- 

 lece (see photographs 6, 17, 23) Hedysareœ and the Genisteœ, the bac- 

 teria are mostly small rods with comparatively few branching and irregii- 

 lar cells. In plants of the tribes Trifoliœ (see photographs 1, 3, 3, 4, 

 5, 8, 9, 10, 13, 15, 16) and Viciece (see photographs 12, 13, 14, 18, 20, 

 21, 22), branching in irregular forms prevail. The simple rods general- 

 ly but not always prevail in young nodules and in small nodules, where- 

 as branched and irregular forms are more often observed in older and 

 larger nodules. The proximal part of the nodule, the part first formed, 

 may contain simple rods mainly, and the distal part, where growth is 

 taking place rapidly, may contain simple rods and many branched and 

 twice branched forms. WTiere general infection of the leguminous crop 

 occurs, the bacteria may be mostly rods or mostly branched forms the 

 same as in nodules (see Hask cultures and photograph 22). 



Hanging drop preparations from pure cultures on agar and liquid 

 media have been observed at different stages of growth. From agar 

 cultures the cells are short or longer rods, mostly single but some are 

 joined end to end in twos with rounded ends, often larger at one end, 

 often bent or curved or swollen at the middle. Internal^, the proto- 

 plasm is seen to l>e of unequal density and shows bands or plates of dens- 

 er protoplasm with more transparent portions between. The cells are 

 swiftly and actively motile, darting, whirling and tumbling; they are 

 especially active from young cultures and when the hanging drop is first 

 made. In preparations from older cultures, fewer motile cells are seen, 

 but some may be seen in motion as long as the culture shows any in- 

 crease in growth. 



