CHAPTER XVII. 



DICOTYLEDONS. 



THE second sub-class of the angiosperms, the dicotyledons, 

 receive their name from the two opposite seed leaves or coty- 

 ledons with which the young plant is furnished. These leaves 

 are usually quite different in shape from the other leaves, and 

 not infrequently are very thick and fleshy, filling nearly the 

 whole seed, as may be seen in a bean or pea. The number of 

 the dicotyledons is very large, and very much the greater num- 

 ber of living spermaphytes belong to this group. They exhibit 

 much greater variety in the structure of the flowers than the 

 monocotyledons, and the leaves, which in the latter are with few 

 exceptions quite uniform in structure, show here almost infinite 

 variety. Thus the leaves may be simple (undivided) ; e.g. oak, 

 apple ; or compound, as in clover, locust, rose, columbine, etc. 

 The leaves may be stalked or sessile (attached directly to the 

 stem), or even grown around the stem, as in some honeysuckles. 

 The edges of the leaves may be perfectly smooth (" entire "), or 

 they may be variously lobed, notched, or wavy in many ways. 

 As many of the dicotyledons are trees or shrubs that lose 

 their leaves annually, special leaves are developed for the pro- 

 tection of the young leaves during the winter. These have 

 the form of thick scales, and often are provided with glands 

 secreting a gummy substance which helps render them water- 

 proof. These scales are best studied in trees with large, 

 winter buds, such as the horsechestnut (Fig. 92), hickory, 

 lilac, etc. On removing the hard, scale leaves, the delicate, 

 young leaves, and often the flowers, may be found within the 

 bud. If we examine a young shoot of lilac or buck-eye, just 

 as the lenvcs are expanding in the spring, a complete series of 

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