56 THE STORY OP THE PLANTS. 



swollen, or in an underground stem or root- 

 stock. In most cases, however, perennial 

 plants take care to keep over their live material 

 from one season to the other by some such 

 means of permanent storage. They are, so to 

 speak, capitalists. Natural selection has of 

 course preserved those plants which thus laid 

 by for the future, and has killed out the mere 

 spendthrifts which were' satisfied to live for the 

 fleeting moment only. The soil of our meadows 

 in winter is full of tubers, bulbs, and root- 

 stocks ; while our shrubs and trees carry over 

 their capital from season to season in their 

 living bark, secure from injury. In one way or 

 another all our perennial plants manage to tide 

 their living green-stuff, or at least its raw 

 material, by hook or by crook, over the dangers 

 of winter. 



I have given so much space to the subject of 

 leaves because, as you must see, the leaf is 

 really the most important and essential part of 

 the entire plant the part for whose sake all the 

 rest exists, and in which the main work of 

 making living material out of lifeless carbonic 

 acid and water is concentrated. 



Let us sum up briefly the main facts we have 

 learned in this long chapter. 



Plants eat carbonic acid under the influence 

 of sunlight. They store up the solar energy 

 thus derived in starches and green-stuff in their 

 own bodies. Very simple plants, which float 

 freely in water, eat and drink with all portions 

 of their surface, But higher plants eat with 



