Communications. 265 



the tissueg of the plant. Experiments have been made where 

 diseased and healthy tubers were cut and bound together, and 

 planted, each sending up stalks and growing together, interlaced 

 at root and top. In some instances both plants perished. In 

 others the plant from the diseased tuber rotted down, and the 

 other was partially affected, and in others the diseased one had 

 no effect on the other. ETealthy stalks and tubers grew in the 

 same hill with diseased oneg. IE it is the primary cause, 

 surely it would seem to have been favorably situated in those 

 instances to produce its legitimate result. 



Another fact that points to the same conclusion is that the 

 spores sometimes germinate, sending their mycelium into the sto- 

 mata of the leaf, and then remain dormant for days and weeks 

 even, not making further growth unless there is a change of con- 

 ditions which apparently makes development possible. There 

 are also instances noted where the atmospheric and other outward 

 conditions regarded as essential to the growth of the fungus, are 

 entirely lacking, and yet it grew right along. Put these two 

 points together and do they not indicate, at least, that other agents 

 contribute to, or prevent its development and limit its power. 

 In fact, if a cause at all, that it is controlled by other causes. 



The fact often noticed, that certain varieties are much less apt 

 to be affected by the disease than others, and in some instances 

 can stand in the midst of affected fields and plants where the 

 spores of the fungus must be abundant, and yet receive little or 

 no injury, shows, at least, that there is a resisting power, an innate 

 vitality in them, which limits the power of the fungus, and the 

 further fact, that where the local conditions are favorable to a 

 healthy and vigorous growth, varieties predisposed to the disease 

 will be little affected while in other fields near by they are rotting 

 down, would naturally lead to the conclusion that this resisting 

 power can be increased by adapting outward conditions to the 

 promotion of a strong and healthy growth, or take the converse, 

 that the predisposition, the liability to the attack of the fungus, 

 comes from debility, or loss of vitality in the plant itself. 



This view is corroborated by the results of the experiments 

 Professor Smith already mentioned, in which he bound together 



