THE STRUCTURE AND WORK OF THE STEM 99 





seen in the cabbage, we might say that a bud is a very much shortened 

 branch, or, in reality, " the promise of a branch." 



Factors which influence the Opening of a Bud. A bud responds to 

 the same stimuli that we have seen call a young plant into active Me from 

 the seed. If a branch containing unopened buds (such as horse-chestnut 

 or willow) is placed in water in a moderately warm room, it will respond 

 to the factors without it and begin to open. The tips of branches, still 

 attached to the tree outdoors, may be introduced into a warm room 

 through a hole bored in the window sash. They will open to bear flowers 

 and leaves during the coldest months of the year. The factors which 

 influence the germination of seeds also act on the bud. 



Adaptations in the Bud of Horse-Chestnut. If we now turn our at- 

 tention to horse-chestnut buds which have been previously placed in 

 water to open, we shall be able to get some notion of the wonderful adap- 

 tations of the bud which fit it for its work. 



In the first place, a horse-chestnut bud is covered with a sticky ma- 

 terial. Not only does this covering keep out unwelcome visitors which 

 might bore into the bud and destroy the tender parts within, but it also 

 serves as a waterproof cover- 

 ing against the icy rains of 

 the late fall and early spring, 

 and against evaporation in 

 dry weather. In the unopened 

 buds the scales overlap like 

 shingles on a roof. In buds 

 which have begun to open, we 

 find that not only have the 

 tiny green leaves been pro- 

 tected by the outer scales, but 

 they have been additionally 

 wrapped in soft, cottony sub- 

 stance. The young leaves are 

 always folded or rolled up in 

 the bud. Two purposes are 

 thus served protection from 

 the elements and from drying 

 by little exposure of the deli- 

 cate surface, and economy of 

 space by means of the tight 

 and compact stowing away of 

 the parts thus folded. 



Why Buds are Covered. 



When we consider that most of our earliest green leaves come from open- 

 ing buds in the early spring, the importance of a protective covering is 

 well seen. Nevertheless, buds are frozen time and again during the cold 



Opening bud of horse-chestnut : L., leaves ; 

 L.S., leaf scar; S., scalelike leaves which 

 cover bud. 



