STIPULES AS THORNS 175 



itself develop further. This axillary branch can then 

 be just seen, as a small point, but in other cases it 

 grows out and becomes an ordinary branch. Here 

 again, as in BERBERIS and ZIZYPHUS, protection 

 from grazing animals is afforded to the leaves, by 

 the conversion (or modification) of what are usually 

 soft organs (the stipules and sometimes also the end 

 of the rachis) into hard sharp thorns. And the value 

 of this protection is increased as in BERBERIS by 

 the shortness of some of the axillary shoots, so that 

 the leaves they bear are quite close down among the 

 thorns. At the same time the direct cause of this 

 and other spinous modifications of stipules, leaves or 

 branches is probably the dryness of the air or soil, 

 for when cultivated under very damp conditions these 

 spines often become ordinary soft leaves, etc. 



There are other species of the genus PITHE- 

 COLOBIUM, some 3 have spines, some have not. One 

 species PITHECOLOBIUM SAMAN, though also not a 

 native of India is very common, being often planted 

 along roads as a shade tree. Among Europeans it is 

 known as the * Rain-tree '. 



There are no thorns on this tree, and each leaf has 

 several pairs of pinnae, and each pinna several pairs 

 of leaflets. Being a tree, it carries its leaves high up, 

 and well out of the way of grazing animals, so that 

 thorns are not necessary. You should notice that at 

 the base of each leaflet and each pinna, is a pulvinus, 

 and that at about five o'clock every evening the leaf- 

 lets move downwards, and the pinnae also. The blades 

 of the leaflets, instead of being more or less horizontal, 

 thus come to be nearly vertical, so that while during 



