226 



THE REPRODUCTIVE ORGANS 



they are barbed pappose bristles ; while those of the 

 Burdock (Fig. 160, 5) are hooked bracts. 



(5) In some cases Nuts of various kinds may be collected 

 as food by such animals as mice and squirrels ; and some 

 of these may be left, which then germinate. 



(6) Again, ants are active agents in fruit and seed 

 dispersal, especially in the case of those seeds which have 

 oil-bodies attached to them. This is well seen in the Gorse 

 (Fig. 161, 1), and more clearly still in the Castor Oil seed 

 (2). Similar oil -bodies occur in many plants, e. g. Cow 

 Wheat, Cornflower, and several fruits of Sedges, Rushes, 



1. 2. 



Fig. 161. Seeds with Oil-bodies. 

 I, Gorse ; 2, Castor Oil ; 0, oil-body. 



and Grasses. The ants eat the oil-body, and throw the 

 seeds away ; along an ant-run, lines of such plants may be 

 found grown from seeds which have been dropped by ants 

 on their way to the nest. The process may easily be 

 observed if such seeds are laid in their track. 



D. Propulsive mechanisms. In addition to the modes 

 of dispersal already mentioned, many plants possess 

 devices which render them independent of wind, water, or 

 animals as carrying agents. (1) Often, as the fruit ripens and 

 dries, tensions are set up in the fruit-coat, which result 

 in a sudden bursting, whereupon the seeds are shot out 

 sometimes several feet. 



