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that his observations indicate that it is caused by a nematode. 

 Leibscher found that peas when grown ten times in thirteen years 

 Twith beans three times), on the same land were very stunted. Bj 

 July the plants which had no nitrogenous manure were all dead, whilst 

 those which were manured with nitrogen though still growing were 

 unhealthy. The plants were found to iiave no, or very few nodules, 

 on their roots, whilst similar plants in a rotation had many nodules^ 

 except where nitrogenous manure had been applied, in which case they 

 were less abundant. An attempt to cure pea-sickness by inoculation 

 from a good pea soil had no effect, and it was found that the roots of 

 the unhealthy plants were covered with nematodes. Leibscher then 

 grew about 100 varieties of plants of a pea-sick field, and obtained the 

 following remarkable result. All the peas, and some varieties of vetch, 

 had swarms of nematodes. Other varieties of the vetch, chick-peas 

 (Kicher), Lathyrus Cicera and Cicer arietinum had fewer nematodes. 

 The three kinds of lupins had very few, whilst Phaseolus, and all the 

 various clovers which were growing in the field, had none at all. 

 The gramineous and root crops were also free from nematodes. 



The question arises, whether it is not possible that the attack by the 

 nematodes on the plants named was the result, rather than the cause, of 

 the sickness. The fact that peas and vetches were simultaneously 

 attacked by the nematodes reminds one that both these plants grow in 

 symbiosis with the same modification of the nodule bacterium, whilst 

 clover, for instance, which was not attacked in this experiment, requires 

 another modification and lupins which were very slightly attacked, again 

 another modification. This seems to point to the total failure of one 

 particular microbe (or modification, as the case may be) as the cause of 

 failure of the corresponding plants ; and the presence of nematodes 

 on the roots of the peas and vetches might merely be due to decaying 

 vegetable matter, as being to them a more suitable kind of food than 

 the healthy roots of other plants. The fact that in liebscher's first ex- 

 periments the manured portion of the field suffered less than the 

 un manured would then indicate that the nitrogen supplied enabled 

 the plants to at any rate keep alive without the symbiosis, and thus, to 

 some extent, resist the attacks of the nematodes. We have a somewhat 

 similar case in the clover experiments at Rothamsted. In a rich garden 

 soil, thirty-seven cuttings of clover were obtained in twenty years 

 (being resown only four times), whilst on arable land close by, it will 

 not grow even once eveiy four years in a rotation. Leibscher's view, 

 that the peasickness was caused by nematodes, involves the assumption 

 that clover has a special nematode, since it was not attacked in the least on 

 the pea- sick land. The theory of the failure being due to the absence 

 of the pea (or vetch) micro-organism is consistent with the fact that 

 clover did not fail ; since clover requires, and no doubt had, its own 

 particular modifications. Against this we have the fact that inoculation 

 with pea soil failed to cure pea-sickness ; and this might be due to 

 accident. The results are full of interest, and the question deserves 

 thorough investigation. 



Although it has been shown that adequate inoculation of the soil ia 

 essential, it has been as clearly illustrated that a greatly increased 

 growth of leguminous plants cannot be attained without a liberal supply 



