TlIJC LEAF 



73 



55. Leaf of the Quince; 

 h, blailc; p, peti- 

 ole; st, stipules. 



ments are also conduits of water and of tlie 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 tlie active green tissue, assur- 

 ing an abundance of water. Tiiat water tliroughout the 

 wliole 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, tlie leaf has 

 three parts, — the petiole, or stalk, a 

 pair of stipules at the base of the jjeti- 

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



110. Stipules. — In the majority of 

 leaves stipides are quite wanting; if 

 produced at all, tliey are in many cases 

 soon lost. In the Pea, however, where 

 tlie terminal jiart of the blade is converted into a tendril, 



the stipules are large and take part in 

 assimilation. Ordinaril}', 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 IJegonia (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 tlie 

 nature of stipules. The cliief use of 

 stipules is, then, protective. 



111. A special modification of .stipules to serve 

 quite other use.s is seen in the case of the prickles 

 of the Locust (Fig. 50). 



112. In Acacia s/xii/icigern the stipules are 

 5(j. Stipules of ilie (Jeveloped as hollow tliorns, au inch or more in 



Locust tree, (le- i .u i • u i ii. j i- i c 



, , . length, which become the dweiimo- places ot cer- 



veloped as pnc- & ' ^ o i 



Itles. 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- 



