886 ECOLOGY 



reproduction. The length of this initial vegetative period differs widely, 

 varying from a few weeks in certain xerophytic annuals to a number of 

 years in the century plant and in most trees. There may be but one 

 reproductive period following this initial vegetative period, as in annuals 

 and biennials, and in such perennials as the century plant ; in these 

 forms, which are known as monocarpic plants, death follows fruit matura- 

 tion. In most perennials, however, reproduction either continues in- 

 definitely after its inception or more often recurs at certain periods, 

 vegetative activity also continuing indefinitely or periodically ; such 

 forms are termed polycarpic plants. The most representative poly- 

 carpic plants are trees and shrubs, in which the shoots do not die down 

 after flowering; in rhizomatous and bulbous plants, however, each shoot 

 dies soon after flowering, much as in annuals, and new shoots arise by 

 vegetative reproduction. 



Probably in the majority of the perennials of temperate climates, the 

 vegetative and reproductive periods, to some extent at least, alternate 

 with one another, the flowering period being rather sharply defined, and 

 often of short duration. Excellent cases of such alternating periods occur 

 among plants with vernal flowers, as in the willows and poplars, and in 

 such herbs as Hepatica and Sanguinaria, which bloom before vegeta- 

 tive activity begins. In such plants reproductive activity merely ap- 

 pears to antedate vegetative activity, early flowering being possible 

 only because of the food accumulated during the previous season; for 

 that matter, the reproductive period in such plants begins in the spring 

 or in the summer previous to flowering, and in some cases (as in the 

 alder and hazel) the buds are fully formed before winter begins (fig. 

 1234). In many plants the spring and summer are periods of vegeta- 

 tive activity (as in the goldenrods, asters, gentians, and witch-hazel), 

 while the reproductive period falls in the late summer or in autumn. 

 In some plants (as Satureja and Lechea) there are strongly marked vege- 

 tative periods in spring and in autumn, separated by the summer repro- 

 ductive period. An unusually sharp contrast between vegetative and 

 reproductive activity is afforded by the wild leek (Allium tricoccum) 

 and by the meadow saffron (Colchicum autumnale), in which the leaves 

 appear in spring and soon die down, while the flowers do not appear 

 until summer or autumn. 



There are many species in which the vegetative and reproductive 

 periods are essentially coincident. In a few instances (as in Dicentra 

 and Claytonia) the two periods not only are more or less coincident, but 



