68 Flowers and their Unbidden Guests. 



them now tried to escape by getting, as best they might, 

 to the edge of the leaf, and letting themselves fall 

 from thence to the ground. Some succeeded, but 

 others tried this method of escape too late ; for the 

 air soon hardened the milky juice into a tough 

 brown substance ; and after this aU the strugglings of 

 the ants to free themselves from the viscid matter 

 were in vain. Their movements became gradually 

 fewer and weaker, until finally they ceased altogether, 

 and the dead animals were left adhering to the in- 

 volucre or the uppermost leaves. 



I do not hesitate to infer from this observation 

 that the presence of milky juice in certain parts of 

 plants is to be regarded as another of the appliances 

 by which flowers are protected from the unwelcome 

 visits of creeping animals ; and I find a further support 

 for this view in the fact that the leaves and the inter- 

 nodes in the various species of Lactuca and Asclepias 

 contain a larger abundance of mUky juice the nearer 

 they are to the flowers. Creeping insects can ascend 

 without any difficulty over the lower leaves and lower 

 parts of the stem of these plants ; for the passage of the 

 little creatures over these parts causes no discharge of 

 milky juice. It is only when they come nearer to the 

 nectariferous flowers, intended, as these are, for flying 

 insects, that their sharp booklets cut into the turgid 

 epidermal cells, and that the mUky juice is discharged 

 in streams from the rents thus made. It is further 



