Feb 1897.] BOTANICAL SOCIETY OF EDIXBUEGII 33 



Question 2. — Hellriegel experimented with sterilised 

 soil, and grew his plants with the conditions — no nitrogen 

 and non-inoculated, and no nitrogen but inoculated. Of 

 greater complexity are the experiments of Nobbe and 

 Hilltner, who added to some of the sterilised soils (left 

 sterilised or else reinoculated) varying proportions of 

 nitrogen, and noted results. Their answer to Question 2 

 is, that the effect of the nodule reaches its full worth when 

 the soluble nitrogen of the soil is almost used up by the 

 growing plants. The more a soil contains of bound 

 assimilable nitrogen so much the later will the differences 

 stand out externally between inoculated and non-inoculated 

 plants. Quickly-growing leguminous species, like peas and 

 vetches, which sooner exhaust the supply of combined 

 nitrogen, will show the effects of inoculation earlier than 

 clovers or lathyrus, which, growing at first more slowly, 

 make more trifling demands on the soil nitrogen. 



Question 3. — Do the bacteria from the nodules of 

 different leguminous plants belong to one and the same 

 species ? Beyerinck is of opinion that the bacteria culti- 

 vated from the different species of Leguminosas are not 

 identical, though certainly very similar. He distinguishes 

 two groups : (1) Those whose large colonies are more 

 hyaline and give rise to bacteroids, forked or roundish. 

 Such are bean, vetch, broom, medicago, melilotus, clover, 

 pea, lathyrus. (2) Those with opaque, dull white colonies 

 giving bacteroids seldom branched, but more like bacteria, 

 e.(j. ornithopus, lotus, lupinus, robinia, caragana. Xobbe 

 and Hilltner believe that though the bacteria springing 

 from the different leguminous species can scarcely be 

 distinguished from one another externally, yet in their 

 effect and behaviour and attitude to the plants they 

 show noteworthy differences. For example, bacteria won 

 from nodules on the pea, infect most powerfully other pea 

 plants, and act most beneficially on them ; infect and act 

 less favourably to plants not peas, but closely related to 

 them, but produce no impression on leguminous species like 

 robinia or clover, whose affinity with the pea is not close. 

 Vice versa, bacteria from the nodules of the red clover 

 infect other red clover plants, but are quite ineffectual on 

 peas. 



TRANS. EOT. SOC. EDIX. VOL. XXI. T> 



