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 Dahlia-roots. 
with food made by last year’s vegetation, nourish in 
spring the buds on the base of the stem just above 
(«, 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 ther 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 
Ground-Artichoke. 
