44 



GLOSS A in" OF 



(c) In certain cases to serve as a storehouse for jjlunt- 

 food. 



C. Phyi.i.omk : including the leaves and all tlieir equivalents, 

 sucli as bracts, cotj'ledons. bud-scales, sepals, petals, etc. , 

 as already' described. 



The phylloine is always developed laterally on a 

 caulome. 



Foliage-leaves (as contrasted with flower-leaves) are 

 generally green, owing to the jircsence of a substance 

 called chlorophi/ll (found also in all other gi-een parts). 

 A section thi-ough the body of a leaf is shown in Fig. 

 245, the shaded portions I'epresenting the cells v^^hich. con- 

 tain , Iilorophyll. 



The chiet function of foliage-leaves is to assimilate the 

 food-naaterials derived from the soil and the air, thus 

 converting them into forms (commonly starch) which can 

 be used in advancing the plant's growth. Sunlight and 

 chlorophyll are essential to the process of assimilation. 



Transjnratioyi. Water-vapour is given off through 

 the leaves, by the agency of minute openings (chiefly on 

 the under surface) known as stomata (singular stoma). 

 One of fhese greatly magnified is shown in Fig. 246. 

 These stomata communicate with air-spaces among the 

 loosely-packed cells in the body of the leaf. It may often 

 be observed in hot bright weather that the leaves of plants 

 droop if exposed to the sun ; this is because the loss of 

 water through the leaves is greater than the suj^ply 

 through the roots. At night, however, the stomata close, 

 and the balance being restored the plant recovers. 



The functions of flower -leaves have already been re- 

 ferred to. 



D. — Triciiome : including all the outgrowths from the surface 

 or epidermis, whether of stem, leaf or root, such as hairs, 

 bristles, root-hairs, prickles, etc. 



Of all the trichoma sti-uctures the root-hairs which 

 occur abundantly on the j^oung roots of most plants, are 

 the most imjiortant. They consist of single long cells, 

 and their function is to increase the absorbing surface of 

 the root, for which service they are peculiarly fitted by 

 the thin and delicate nature of their walls. 



Hairs on parts above ground usually consist of a row 

 of cells placed end to end (Figs. 247, 248). Often they 

 are branched, as in the leaf-hairs of the ]\Iullein. 



Glandular hairs secrete a liquid in the cell which oc- 

 cupies the extremity of the hair. The sticky surfaces of 

 certain plants are produced in this way. 



^□□□coqt 



'■^^ 



Fifr. 2-17. 



Fig. 218. 



