Exclusion of Snails and Soft Insects. 1 5 



Of the Gasteropods, the voracious Helicidse are espe- 

 cially dangerous and unwelcome visitors. They are, 

 however, to be found, comparatively speaking, but rarely 

 upon the flowers. This is not because the perianth- 

 leaves are distasteful to them, but because they can be 

 kept off more easily than other uninvited guests. A 

 simple group of bristles or prickles on any part of the 

 plant that has to be traversed by the snail in order to 

 get at the flower is enough to prevent its further ad- 

 vance. It avoids most carefully, all contact between its 

 soft, easily injured body and the points of a bristle or 

 a prickle ; and, if it . comes to a place so protected, it 

 turns back at once, without any further attempt to 

 overcome the dif&culty. The same holds good for such 

 insects as have soft bodies, and especially for numerous 

 caterpillars, many of which would readily devour the 

 perianth-leaves, or those which go to form the gynsecium, 

 if they were not debarred from access to the flower. 



I once also noticed that caterpillars sought out 

 the just-opened tubular flowers of the garden Penta- 

 sfemon gentianoides, as a corner protected from wind 

 and weather, therein made their webs, and underwent 

 their transformation, whereby the reproductive pro- 

 cesses were rendered impossible in the flowers in 

 question. Probably in those places where the Penta- 

 stemon grows wild, it is not exposed to such visitors. 

 Nevertheless this observation is worth mentioning 

 here, as it makes one suspect that the reason, why 



