42 HABITS OF WOKMS. Chap. I. 



on a wall were so tough that they could not 

 be gnawed by worms, but after four days 

 they were affected in a peculiar manner by the 

 secretion poured out of their mouths. The 

 upper surfaces of the leaves, over which the 

 worms had crawled, as was shown by the dirt 

 left on them, were marked in sinuous lines, 

 by either a continuous or broken chain of 

 whitish and often star-shaped dots, about 

 2 mm. in diameter. The appearance thus pre- 

 sented was curiously like that of a leaf, into 

 which the larva of some minute insect had 

 burrowed. But my son Francis, after making 

 and examining sections, could nowhere find 

 that the cell-walls had been broken down or 

 that the epidermis had been penetrated. 

 When the section passed through the whitish 

 dots, the grains of chlorophyll were seen to 

 be more or less discoloured, and some of the 

 palisade and mesophyll cells contained 

 nothing but broken down granular matter. 

 These effects must be attributed to the trans- 

 udation of the secretion through the epidermis 

 into the cells. 



The secretion with which worms moisten 

 leaves likewise acts on the starch-granules 



