122 THE NATURE AND WORK OF PLANTS 



and allowed to remain out of doors in the cold until 

 the first of December, then put in a cellar for a 

 month or two, they may then be potted and will 

 begin to grow. Note the behavior of the bud cover- 

 ing. It does not burst open immediately, but elon- 

 gates until it reaches the surface of the soil, and then 

 only does it open and expose the young leaves. Set 

 the pot with the growing bud in a dark room, or 

 cover it with a pUe of moss. The bud wUl con- 

 tinue to elongate until it reaches the light, or it has 

 attained a length of seven or eight inches, which 

 seems to be its limit of growth. Its purpose is to 

 bring the leaves above the surface of the ground, and 

 it does not open until it is struck by the light, which 

 is usually a signal that this has been accomplished. 



170. Some protective devices of the shoot. — 

 Leaves and stems are subject to destruction by 

 animals which use them for food, and a large 

 number of species are furnished with structures 

 which hinder or prevent attack by the animal. The 

 most common means of protection consists lq poison- 

 ous or bitter substances in the tissues, spines, prickles, 

 bristles, thorns, and stinging hairs. 



The acrid burning sensation which follows tasting 



