1914 EXTUMULOGIUAL SOCIETY. 97 



out ill any State, as a jiart of an extended plan of work, notably that of wheat 

 sowing in fall to evade the fall attack of Hessian fly, we have carried out such 

 experiments with the co-operation of farmers at whatever points seemed most desir- 

 al)le for obtaining results which would benefit the greatest number of farmers. Id 

 many cases these sowings have been also made in co-operation with State institu- 

 tions. The alfalfa weevil investigation have been carried on in co-operation with 

 the State agricultural college and station at their request. 



Besides tlie Held laboratories there are being carried on field experiments, out 

 on the farms, under precisely the same conditions as those which the farmer has 

 himself to meet. These experiments are conducted in such a way that farmers can 

 see just what is done, how it is done, as well as the object of the experiment itself. 

 They can also see what results are obtained, and what we have done, under their 

 conditions, they, under like conditions, can do for themselves; and the proof thereof 

 is right liefore their eyes in their own fields. We find that these object-lessons and 

 jtcrsonal contact are primarily worth vastly more than whole volumes of literature, 

 and gradually the farmer is coming to learn that there is help for him as well as 

 for the horticulturist, in combating insect pests, even though his acreage may be 

 many times theirs and his crops radically different in nature. 



IXSECT GALLS. 



By a. Cosens, Ph.D., Toroxto. 



(Abstract of Lecture, illustrated bj^ lantern slides.) 



In the evolution of the study of galls there are different epochs, each 

 merging gradually into the following. From early historical times these abnormal 

 structures have excited attention. In the first instance, this was in all probability 

 due to the fact that they presented plienomena unusual and out of the ordinarv. 

 At this earliest epoch witchcraft and like fanciful explanations were proposed to 

 account for their origin. Gradually, as tliey were better understood and seen to 

 involve a stimulus by a parasite and a response by a host, the examination of 

 them became more scientific, and the hypotheses concerning their causes, as a 

 consequence, more valuable. Tlie problem presented was recognized as one of 

 great scientific interest, since it presented the unique feature of a foreign organism 

 stimulating and controlling for its own benefit the growth of a host. Within the 

 last few years it lias been shown that a close relation exists between the structure 

 of the bacterial crown gall and certain malignant animal tumors. Thus the second 

 epoch with the subjects of theoretical interest seems gradually to be passing into 

 a third in wliich it will rank as one of the greatest practical importance. 



The term "gall"' is applied to any enlargement of plant cells, tissues, or organs 

 induced by the stimulus of a parasitic organism as a regular incident in the life 

 history of the parasite. 



Galls are divided into two classes, according to the agent that produces the 

 stimulus — namely, Pliytocecidia, those owing their origin to parasitic plants, and 

 Zoocecidia. those produced by animal parasites. The former are caused by many 

 different classes of plants, myxomycetes, bacteria, algre and fungi. Even the 

 flowering plants are represented among the gall producers, since the witches' 



7 E.S. 



