CH. Ill, 2] STRUCTURE OF LEAVES 17 



thin, flat, and greened perform the functjpjj_oQooH forma- -. 

 _ tion, other kinds exhibit cutterent leatures~~and other func- 

 ^ tions, as familiar, for instance, in tendrils and pitchers. 

 Likewise there are parts which seem to be leaves but are not, 

 as in case of some flattened stems, and even roots ; for leaves, 

 while the principal, are not the only green parts of plants. 



2. THE STRUCTURE OF LEAVES 



Typical, or foliage, leaves, despite their external multi- 

 formity, possess an essentially uniform anatomical struc- 

 ture, as shown by comparative observation. 



The most conspicuous and important part of the leaf, that 

 in which the food is formed, is the green tissue, called CHLQ-I 

 ^RENCHYMA, which is singularly uniform in thickness, texture/ 

 and color throughout the leaf blade. Its distinctive green! 

 color is not, however, an integral part of its structure, buti 

 a separate and easily removable substance. One has onlyj 

 to place a leaf in a glass dish, cover with alcohol, stand in 

 a warm place, and leave for a time, when the green will 

 come out in a beautiful clear solution, leaving the leaf a 

 uniform white, ^his soluble ffreen snbsta.ncp is 

 CHLOROPHYLL, SgldlS One J)f JJ?P n}^s 



willpresently appear. 



^ 



Second in prominence is the system of ^VEINS, which 

 ramify everywhere throughout the chlorenchyma. Thoj^ 



r>f - tnfces which conduct materials 



r>]]f, ftf the chjorenchyma. Most commonly they 

 taper and branch from the base of the blade towards the 

 margin, simultaneously producing small veinlets which 

 interlace to a network, as seen very clearly when held up 

 against the light. In other kinds of leaves, such as Grasses, 

 the main veins are uniform in size, and run parallel, or 

 gently curving from base to tip, the veinlets in this case 

 being minute or even wanting ; and such leaves are called 

 i n distinction from the former, 



_ VEINED kinds (compare Figs. 1 and 2 with 34). If, further, 



