MODE OF LIFE IN PERENNIALS. 



29 



leaves and in the short stem or stalk. These accordingly become thick and nutri- 

 tious in the Cabbage, just as the root does in the Turnip, or the base of the short 

 stem alone in Kohlrabi, or even the flower-stalks in 

 the Cauliflower ; all of which belong to the same 

 family, and exhibit merely different ways of accom- 

 plishing the same result. 



73. Perennials are plants which live on year after 

 year. Shrubs and trees are of course perennial. So 

 are many herbs ; but in these only a portion gener- 

 ally survives. Most of our perennial herbs die down 

 to the ground before winter ; in many species all but 

 certain separate portions under ground die at the 

 close of the year ; but some parts of the stem con- 

 taining buds are always kept alive to renew the 

 growth for the next season. And a stock of nour- 

 ishment to begin the new growth with is also pro- 

 vided. Sometimes this stock is laid up in the roots, 

 as for instance in the Peony, the Dahlia (Fig. 58), 

 and the Sweet Potato. Here some thick roots, filled 



u 



with food made by last year's vegetation, nourish in 

 spring the buds on the ba«e of the stem just above 

 (a, a), enabling them to send up stout leafy stems, 

 and send down new roots, in some of which a new 

 stock of food is laid up during summer for the next 

 spring, while the exhausted old ones die off; and so 

 on, from year to year. 



74. Sometimes this stock of food is laid up in par- 

 ticular portions of branches 

 of the stem itself, formed 

 under ground, and which 

 contain the buds ; as in the 

 Ground Artichoke and the 

 Potato. Here these parts, 

 with their buds, or eyes, are all that live over winter. These thickened ends of 

 stems are called Tubers. In Fig. 59, a is a tuber of last year, now exhausted and 



S9 

 Ground -Artichoke. 



