THE LEAF 



73 



Leaf of the Quince ; 

 b, blade; p, peti- 

 ole ; st, stipules. 



ments are also conduits of water and of the prepared plant 

 food when this is drawn away from the leaf in a liquid 

 form to other parts of the plant. The smallest veinlets 

 penetrate to every section of the active green tissue, assur- 

 ing an abundance of water. That water throughout the 

 whole body of the leaf plays an important part in keeping 

 the leaf elastic and outspread is seen when, from lack of 

 watering, the leaves of plants wilt and 

 droop. 



109. The parts of the leaf. When 

 most highly developed, the leaf has 

 three parts, the petiole, or stalk, a 

 pair of stipules at the base of the peti- 

 ole, and the blade, or lamina (Fig. 55). 



110. Stipules. In the majority of 

 leaves stipules are quite wanting; if 

 produced at all, they are in many cases 

 soon lost. In the Pea, however, where 



the terminal part of the blade is converted into a tendril, 

 the stipules are large and take part in 

 assimilation. Ordinarily, the stipules 

 originate when the leaf is very small, 

 attain their growth early, and overarch 

 and protect the young and tender blade ; 

 or, as in Begonia (Fig. 15), the stipules 

 of each leaf regularly inclose and shield 

 the younger leaves of the shoot. In very 

 many winter buds the scales are of the 

 nature of stipules. The chief use of 

 stipules is, then, protective. 



111. A special modification of stipules to serve 

 quite other uses is seen in the case of the prickles 

 of the Locust (Fig. 56). 



112. In Acacia spadicigera the stipules are 

 the developed as hollow thorns, an inch or more in 



length, which become the dwelling places of cer- 

 kl es . tain small and exceedingly warlike ants. At the 



ends of the leaflets this Acacia bears small food 

 bodies, rich in fat, and in special glands secretes nectar. These mate- 



