HOW PLANTS EAT. 53 



The higher plants, then, have for the most 

 part special organs, the leaves, told off to do 

 work for them as mouths and stomachs ; while 

 other organs are told off to do other special work 

 of their own — as the roots to drink, the flowers 

 to reproduce, the fruit and seeds to carry on the 

 life of the species to other generations, and so 

 forth, down to the hairs that protect the surface, 

 or the glands that produce honey to attract the 

 fertilising insects. To the end, however, all 

 parts of the plant retain the power to eat car- 

 iDonic acid, if necessary ; so that many higher 

 plants have no true leaves, but use portions of 

 the stem or branches for the purpose of feeding. 

 Any part of the plant which contains the active 

 living green-stuff, or chlorophyll, can perform 

 the functions of a leaf. In very dry or desert 

 places, leaves would be useless, because their 

 flat and exposed blades would allow the water 

 within to evaporate too readily. Hence most 

 desert plants, like the cactuses, and many kinds 

 of acacias and euphorbias, have no true leaves 

 at all ; in their place they have thick and fleshy 

 stems, often very leaf-like in shape, and curiously 

 jointed. These stems are covered with a thick, 

 transparent skin or epidermis, to resist evapora- 

 tion, and are protected hy numerous stinging 

 hairs or spines, which serve to keep off the 

 attacks of animals. Stems of this ^ype are used 

 as reservoirs of water, which the plant sucks up 

 during the infrequent rains ; and as they con- 

 tain chloropliyll, like leaves, they serve in just 

 the same way as swallowers and digesters of 

 carbonic acid. 



