Ch. Ill, 9] SPECIAL FUNCTIONS OF LEAVES 



73 



(Fig. 44). The chlorophyll, of course, is all near the surface, 

 and wanting in the interior cells of the chlorenchyma, which 

 increase in number and size, and present a translucent aspect 

 if water is stored, but are opaque if much food is present. 

 Sometimes the upper parts of the 

 leaves become true foliage while the 

 bases alone store food, in which case 

 these storage parts, after the foliage 

 has withered away, form collectively a 

 typical bulb, as in Hyacinth (Fig. 45). 

 In related plants the specialization 

 has gone further, making a division 

 between foliage and storage leaves, in 

 which case the latter become exclu- 

 sively food-storing organs, as in the 

 bulb scales of Lilies (Fig. 46). 



Another form of food-storing leaves, 

 serving also in some cases as foliage 

 and in other cases not, are the coty- 

 ledons or "seed leaves" of embryo 

 plants, later to be fully described. 



In many kinds of plants, some of 

 the leaves deviate in minor features 

 from the typical condition, \n which 

 case they are called collectively 

 bracts. Commonest of all are the 

 little pale scale-like bracts which stand 

 under each flower in a cluster, where apparently they have 

 no function, but represent foliage leaves in an arrested or 

 rudimentary state of development ; for it is a constant struc- 

 tural peculiarity of the higher plants that flowers originate 

 in the axils of leaves, that is, in the upper angle between 

 leaf and stem. Likewise little scale-like bracts occur just 

 below the leaf-like branches of Asparagus and florists' 

 Bmilax (page 195). In the Linden the bract is much larger 

 (Fig. 47), and attached thereto is the flower cluster which 



Fig. 45. — A Hyacinth 

 bulb, in section. The 

 outer or storage leaves 

 are the bases of last 

 year's foliage leaves, and 

 will be replaced, as they 

 wither, by the bases of 

 the new leaves surround- 

 ing the flower cluster. 

 (From Figurier, Vegetable 

 World.) 



