44 



uLuanAjn' OF 



(c) Tn i-t>rf:(in cases to sei've as r\ sfoiplioiiso for plant- 

 food. 



.'. i'liYi.i.nMK : iucluilin^ I lie leaves and all their ciiuivalents, 

 surli as bracts, cotjdedons. bud-scales, sepals, petals, etc., 

 as already described. 



The phyllouie is always developed laterally on a 

 caulome. 



Fol iage- leaves (as contrasted with flower-leaves) are 

 {^nerally gi"een, owing to the presence of a substance 

 called cUlorophyll (found also in all other green parts). 

 A section through the body of a leaf is shown in Fig. 

 245, the shaded portions representing the cells which con- 

 tain ohlorophj'U. 



The ch ief /« /I c^fpn of foliage-leaves is to assimilate the 

 food-materials derived from the soil and the air, thus | 

 converting tliem into forms (commonlj' starch) which can 

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

 chlorophyll are essential to the process of assimilation. 



Transpiration. "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 tliese greatly magnified is shown in Fig. 240. 

 These stomata communicate with air-spaces among the 

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

 be ob.servod 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 supply 

 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- 

 ffiTcd to. 



D. — Tkicmomk: 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 trichome structures the root-hairs which 

 occur abundantly on the young roots of most plants, are 

 tlie most important. They consist of single long cells, 

 and their function is to. increase the absorbing surface of 

 the root, for which service they are j>eculiarly fitted by 

 the thin and delicate nature of their walls. 



Hairs on jiarts aliove ground usually consist of a row 

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

 are branche<l, as in the leaf-hairs of the Mullein. 



Glandular hairs secrete a liquid in the cell which oc- 

 cupies the extremity of the hair. The sticky surfaces of 

 certain idants are pro<luced in this way. 



ziooacziQQc 



Fig. 246. 



"X: 



=^^ 



FlR. 217. 



Kijf. 2W. 



