INFLUENCE OF ENVIEONMENT ON PLANTS 337 



dency to diminish their leaf-surface, probably to reduce 

 evaporation and conserve their stock of water. They often 

 have many of their branches transformed into thorns or 

 spjnes ? and very frequently their leaves show_simjlar reduc- 

 tion. Others which contain little wood are succulent, and 

 their ^surfaces are covered by a very thick and tougQ 

 epidermis, which is strongly cuticularised. Many of those 

 which grow upon rocks have leaves which show special 

 structures for absorbing water from rain or dew. Several 

 species of Saxifrage possess a number of glandular struc- 

 tures upon the teeth of their thick narrow leaves. Each 



FIG. 145. LEAF OF Saxifraga incrustata, SHOWING ABSOBBING\)KGAN. 



consists of a small mass of cells with delicate walls, which 

 lie immediately under the epidermis of a small depression 

 of the surface, and which communicate with the exterior 

 by a few fine pores which perforate the latter. The epi- 

 dermis of this depression is made up of cells with thin 

 non-cuticularised walls. Each so-called gland is in contact 

 with the end of a fibro-vascular bundle, whose sheath is 

 carried forward over the general mass of delicate cells 

 (fig. 145). The depression of the surface is filled with a 

 mass of carbonate of lime, which is originally excreted by 

 the leaf, and which is held in its place by a few papillae 

 which project from the epidermis. Such an arrangement 



