Action of Thrips. 25 



they usually act in the latter manner, the advantages 

 they confer on plants far outbalance the disadvantages. 

 Observations, moreover, that have been made render 

 it very probable that in many cases, owing to certain 

 arrangements presented by the plants, these insects 

 can only pass from one flower, or one flower-head, to 

 another, by a series of continuous jumps. It is with 

 the greatest difficulty, for instance, that they can get 

 across places beset with glandular hairs, and they avoid 

 these most carefully. If placed experimentally on 

 such places, they try to get clear by jumping, but 

 usually are unable to set themselves free, and remain 

 sticking to the hairs, where they soon perish. Thus the 

 glandular hairs which are found so frequently upon 

 peduncles, involucres, and calyces, as also upon certain 

 parts of the corolla, and which we shall have to deal 

 with hereafter as protecting flowers from many crawling 

 animals, probably have reference also to the visits of 

 thrips. 



Completely analogous to this action of the thrips is 

 that of other larger insects. For here again it is the 

 path and the mode of progression by which the flower 

 is reached that determines whether the visit shall confer 

 a benefit or an injury. There are, that is to say, 

 numerous insects, among such as visit flowers and live 

 upon them, which, if they come by flight, are bene- 

 ficial visitors ; but which, if they were not to use their 

 wings, but to gain access by climbing up the stalk 



