STEMS AND BRANCHES AND THEIR USES 217 



tinuously during warm weather, and are then naked ; but 

 when they stop growing, upon the approach of cold weather, 

 they form scales that cover and protect them until the next 

 spring. This, as we have already seen, is the history of the 

 terminal buds of the pine. By tearing apart a winter bud of 

 the horse-chestnut, one gains a very good notion of the struc- 

 ture of buds in general and of scaly buds in particular. On 

 the outside are thick scales that overlap and are held together 

 by a sticky, varnish-like substance that covers their surfaces. 

 The scales within the outer layer are thinner, and those far- 

 ther in are more and more like ordinary leaves ; in the center, 

 finally, are the small, delicate leaves that will spread out and 

 become green when the bud opens. In the spring the sticky 

 substance that holds the outer scales together becomes soft, 

 the scales separate and turn back, and the inner part of the 

 bud grows out into a leaf -bearing branch. The scales and 

 their varnish-like covering not only protect the young inner 

 parts of the bud against the cold, but also prevent the evap- 

 oration of water from the bud. This is important at a time 

 when, as in the winter months, the roots cannot obtain water 

 from the soil. 



235. Induced Growth of Buds. In most plants only a 

 very small proportion of the axillary buds actually develop 

 into branches. If the terminal bud of a stem or branch dies 

 or is destroyed, the axillary bud or buds just below the termi- 

 nal one commonly grow out into a long branch or branches. 

 This happens regularly in many shrubs. For example, all 

 the terminal buds of the lilac die each fall ; in the spring the 

 two uppermost axillary buds of each shoot which are di- 

 rectly opposite each other grow into upright branches. 

 If the end of the shoot, including its upper axillary buds, is 

 killed or cut off, some of the axillary buds below the killed 

 region will grow into branches. As has been said, gardeners 

 remove the tips of cucumber shoots to induce the plants to 

 branch more freely than they otherwise would, and so to pro- 



