1894.] 153 



theless, undoubtedly nibble tliem, and we may, therefore, conclude 

 that in this way it gains access to the vascular bundles and so to the 

 general current of the circulation. On the other hand, the veinlets 

 appear to be quite untouched by the Lithocolletis larva, and conse- 

 quently the entrance of any animal product into the sap stream becomes 

 difficult, if not impossible. In the one case, then, I imagine that the 

 preservative is applied indirectly, through the current of the circula- 

 tion, and in the other case, directly to the cells themselves, by which 

 it is at once appropriated and prevented from spreading farther. 



If this view be correct, if some product of the larva be the real 

 efficient cause, and mechanical irritation but at best a subsidiary one, 

 then it seems to me that this curious condition of the leaf has much 

 in it that allies it with gall formation, especially as seen in the Gynipidce, 

 in which the poison is provided by the larva and not by the parent 

 insect at the time of oviposition. I am aware that Mr. Cameron, when 

 discussing the nature and origin of galls in his " Monograph of the 

 British Phytophagous Hymenoptera,^' vol. iv, issued by the Eay Society, 

 gives his decision against any special poison, and ascribes their forma- 

 tion to mere mechanical irritation. But it is hard to imagine that 

 irritation by itself can give rise to such complicated forms, and of such 

 endless variety, as are presented by galls. Granted, however, a poison, 

 and then the formation of an organized body, a new birth as it were, 

 from the union of the vegetable cell with the animal product, becomes 

 to some extent understandable, with its independent life, carried on 

 in some instances months after it has been shed by the parent plant, 

 as is evidenced by its continued growth and development whilst lying 

 free and exposed on the naked ground. Of course the action of the 

 Lepidopterous larva on the leaf stops very short of this, yet the dif- 

 ference, I fancy, is rather one of degree than of kind. For, in the 

 first place, there is the existence of a substance, the product of the 

 larva. In the next place, this substance is of such a nature that it 

 can be assimilated by the plant tissues. And lastly, although no new 

 growth results from this union of the vegetable cell with the animal 

 product, yet there follows from it a sort of independent life almost as 

 pronounced as in the case of the gall. Let me give an instance of 

 this that made a great impression on me at the time. On August 15th 

 in the past year, at the very hottest period, be it noted, of the late 

 extraordinary summer, I picked up on the side of a steep bank exposed 

 to the full force of the sun, many brown oak leaves holding one or 

 more of the little green patches of suhhimaculella. The leaves were 

 dead beyond all doubt, shrunken, and so dry as to crackle when bent, 



