264 PLANT-LIFE 



place we find hairs and dry scales. Very frequently the 

 stems are protected from the ravages of thirsty animals 

 by a complete armoury of spines. In high latitudes and 

 on Alpine heights, where absorption of water is not 

 possible for long periods because of the frozen ground, 

 there is the same need for such plants as grow there to 

 conserve their water-supply. They really flourish under 

 conditions that are physiologically desert-like. Land 

 plants that grow on the seashore must also avoid exces- 

 sive transpiration. In their habitat it is frequently a 

 case of " Water, water everywhere, nor any drop to 

 drink," for they object to salt-water, and decline to 

 absorb it, and depend upon such rain-water as they can 

 obtain from ground which does not usually retain fresh- 

 water in great quantity. Some such plants have met 

 the peculiar conditions of their environment by develop- 

 ing succulent stems and leaves; the Sea-Eocket {Cakile 

 maritima), Sea-Purslane {Arenaria feploides, Plate 

 XLIV.), and Saltwort {Salsola kali) are examples. The 

 Scentless Mayweed (Matricaria inodora), when it grows 

 on the sea- coast, becomes quite fleshy, in striking con- 

 trast to its inland condition; the same phenomenon is 

 observable in other land-plants growing under similar 

 conditions. 



The due regulation of transpiration in land-plants is 

 of the utmost importance, and it is accomplished by 

 various means. In some circumstances the process 

 needs every encouragement, while in others it must be 

 retarded. When plants grow in a humid atmosphere, 

 transpiration is encouraged by enlargement of leaf- 

 surface, which, of course, involves a vast increase in the 

 number of stomata. Coltsfoot (Tussilago) and Butterbur 



