FROM THE ATTACKS OF ANIMALS. 145 



yielding, like the skin of man and beasts, the 

 cell-contents are poured into the wound. If many 

 stinging hairs side by side be pressed into the skin, 

 there follows redness, swelling, and violent pain, 

 from the poison contained in the cells. Grazing 

 animals avoid plants with stinging hairs most 

 carefully. 



All the plants which we have mentioned belong 

 to the group of forms where the green tissue itself 

 possesses its weapons of defence. With this group 

 we may contrast another where the defences are 

 formed by neighboring members of the plant. To 

 this second group belong those plants, the side 

 branches of which are metamorphosed into woody 

 thorns, which protect the unarmed leaves from 

 attack. The stem and branches of these plants 

 are not leafy to their ends. If there is any trace 

 of leaves on the ends of the branches, they are 

 small, scaly, and anything but an attractive food. 

 The end of the woody branch is sharp and runs 

 out into a pointed thorn. Here the work of 

 defence is carried on by a division of labor. The 

 green leaves can carry on their office undisturbed, 

 under the protection of the thorns. An example of 

 this may be seen in Cytisus spinosus (Fig. 40, 5). 1 



1 A plant belonging to the same genus as the cultivated Laburnum. 



