136 



A TEXTBOOK OF BOTANY 



[Ch. IV, 4 



the Horse Chestnut, for instance, well illustrates (Fig. 75). 

 The scales, which are modified leaves of the preceding 

 year's growth, though prominent, are not an essential part 

 of a bud, having only the temporary function of protecting 

 it over winter, after which they fall. The scales are lacking 

 from all summer buds and some winter ones. The really 

 essential feature of a bud is the embryonic stem composed 

 of meristem or active growth tissue, together with the 



Fig. 90. — A head of Lettuce, in section, illustrative of bud structure ; 

 X 5. (From Bailey.) 



nascent leaves which grow out laterally therefrom. The 

 lower and older leaves of a bud commonly overlap and cover 

 the upper and younger for a time, but later open out to l)egin 

 their work; and in herbaceous plants a perfect gradation 

 is often apparent between the nascent leaves in the bud 

 and the full gro\Aai leaves of the stem. 



Buds are of all sizes, from too small to be seen without the 

 aid of a lens, up to several inches in diameter, as in Palms. 

 A Cabbage or head of Lettuce is essentially a gigantic bud, 

 and offers a particularly favorable illustration of the essentials 

 of bud structure ; for a section made lengthwise through its 



