will become evident at once. If only few at first they will have but 

 little effect until several generations have developed, but this does 

 not require a very long time. We feel very sure that more damage 

 is caused to greenhouse plants by Heterodera radicola than is gener- 

 ally supposed. Working as it does in the roots of the plant and 

 frequently producing even there very slight indications of its pres- 

 ence, plants might, and doubtless often do, linger along and finally 

 die while the cause of the trouble is vainly sought above ground or 

 in the soil, without its real location being suspected. If the roots 

 were examined the casual observer might fail to notice anything 

 unusual in some kinds of plants, even though they were badly 

 affected. In all cases, therefore, where greenhouse plants become 

 unhealthy and sickly and appear to be gradually d3ang without appar- 

 ent cause, an examination for nematode galls on the roots should be 

 made. 



Galls Due to Other Causes Than Nematodes. 



It must not be understood that all galls or swellings on the roots 

 of plants are due to nematodes. There are other agencies and 

 organisms producing a somewhat similar effect as regards superficial 

 appearance, among which two are the most important. These are 

 two low vegetable organisms, the one (Plasmodiophora Brassicae, 

 Wor.) causing the well known " club root " of cabbage and turnip, 

 and the other, a bacterial organism producing galls or "tubercles" 

 on the roots of plants of the order Leguminosae. Plasmodiophora 

 Brassicae is one of the very lowest plant organisms, consisting 

 simply of a homogeneous mass of protoplasm or plant substance 

 and having no distinct parts, organs, or tissues. It lives as a para- 

 site in the roots of the cabbage, turnip, kohl rabi, radish, shepherd's 

 purse, and other plants of the order Cruciferae, and produces an 

 effect sometimes very similar to that of the nematode. We have 

 seen roots of tomato affected by nematodes and those of cabbage 

 with " club root," which could not be told apart except by the odor 

 of the cabbage or by microscopic examination. The two things, 

 however, are quite distinct, having nothing in common except their 

 general appearance. The club root organism enters the root in the 

 form of minute spores and then increa.ses in bulk so as to cause a 

 distension of the cells and consequent enlargement of the root into 

 "clubs." Its effect can usually be distinguished in this locality from 



