THE SHOOT. 95 



to die at the close of the growing season, an underground 

 portion really survives, and sends up the neu- shoots. Such 

 plants, if they live for two years, are called biennials ; or, 

 if they live for several or many years, are called perennials. 



Fig. io8, — Shoots of V'ella spinosa^ sho\\-ing ihorns. Natural size. — After Kemer. 



The shoot may be composed mainly of soft tissues, and 

 persist imderground, where it is protected against unfavorable 

 conditions, such as drouglit and cold, and esiiecially against 

 sudden changes ; or it ma\' be composed mainly of mechan- 

 ical tissues, and be fully exposed, as are the shoots of trees. 

 In these cases the lea\'es generally perish and drop oft an- 

 nually, but in the " e\ergreen " plants they li\e moie than 

 one growing season. 



i/^ 



