Decline of Growth and the Rest Period. 105 
convenient. Seeds that do not germinate well until the 
second spring after maturity (165) are commonly left in 
stratification until that time. 
Section XIV. THE DECLINE OF GROWTH AND THE 
ReEst PERIOD 
171. Annual plants usually perish soon after maturing 
their seed. In other plants, a certain period of vital ac- 
tivity is followed by one in which growth gradually declines 
until it almost or entirely ceases. In woody plants, 
the cells become thickened and a part of the rudi- 
mentary leaves change to bud-scales, which inclose the 
growing point (128). In deciduous trees and shrubs, the 
chlorophyll and starch, with most of the potash and phos-— 
phorie acid contained in the leaves are withdrawn into the 
woody parts, while the leaves themselves are detached and 
fall. The root-hairs also die, in many if not all plants. 
In perennial herbs, the nutritive matters in the foliage and 
stem are withdrawn to the underground parts. A period of 
almost complete repose ensues, during which the plant, 
owing to the dormant condition of its protoplasm, is able to 
endure without harm, extremes of temperature or dryness 
that would be fatal in its active state. 
172. The Rest Period is Not Peculiar to the Temper= 
ate Zones, but occurs in the tropics as well. It cannot be 
ascribed wholly to the change of seasons, as a few familiar 
examples will indicate. Tubers of the earlier varieties of 
the potato, that ripen in the northern states by the begin- 
ning of August, do not sprout if left in the ground till Oc- 
tober, but if stored in a cellar, during winter, at a tempera- 
ture little above freezing, often begin to sprout in March. 
Bulbs of the crocus, tulip, narcissus, crown imperial, etc., 
aE 
