116 



SCIENTIFIC AGRICULTURE. 



Fig. 33. Leaves are opposite when placed at equal 



distances in pairs on opposite sides of the stem. 

 Fig. 33. 



These are the principal forms of leaves; 

 still, many other names are given by botanists 

 to the various modifications of these. Specific 

 terms are employed also in describing the 

 stem, margin, base, point and surfaces of leaves. 

 There are also various appendages to the 

 leaves, which have distinctive names,- in sys- 

 tematic works on botany. To describe all the 

 minor points in the organography of plants 

 would exceed our limits, and, besides, it would render this 

 brief outline of botany too complex to be interesting to the 

 general reader. 



MINUTE STRUCTURE OF THE LEAF. 



The frame work of the leaf is an extension and expansion of 

 the medullary sheath, which is composed of woody fibre and 

 vessels. The integument, or outer covering of the leaf, is 

 the same as that of the bark, of which it is a continuation. 



The cellular tissue peculiar to the leaf is called its paren- 

 chyma. This parenchyma exists in two layers of cells, which 

 differ somewhat in structure. Within the cells, and adhering 

 to their walls, are the minute green particles of cklorophylle, 

 F*g 34. which give color to the leaf: the empty 



spaces between the cells communicate 

 with the external air by means of sto~ 

 mata, or mouths, which, in most plants, 

 are found only on the lower surface. 

 In all those plants whose leaves are 

 vertical, as the iris, they are on both 



[Fig. 34. Magnified sides equally: in the water lily, they 

 section of the epidermis . , . ., /. * ,-, 



of the m y> showing tte exist only in the upper surface, the 



storoata, c, >c. 



lower surface being in contact with the 



