110 Principles of Plant Culture. 



potash and phosphoric acid contained in the leaves, are 

 withdra\v-n into the woody parts (127 ), whUe the leaves 

 themselves are detached and fall. The root-hairs also 

 die in many, if not all i)lants. The leaves of many trees 

 and shrubs assume striking colors as they approach ma- 

 turity. In perennial herbs, the nutritive matters in the 

 foliage and stem are -nithdrawn to the underground 

 parts. A i^eriod of almost complete repose ensues, 

 during which the plant owing to the dormant condition 

 of its protoplasm is able to endure, without harm, ex- 

 tremes of temperature ( ir dryness that would be fatal in 

 its acti\"e state. 



Growth ceases in many trees and shrubs earlier than is 

 often supposed. Most orchard and forest trees of mature 

 age grow little, if any, after midsummer in the temper- 

 ate zones. Cultivation, mulching and manuring tend to 

 prolong the growth period (200). 



172. The Rest Period is Not Peculiar to the Temperate 

 Zones, but occurs in the tropics as well. It can be as- 

 cribed in part to the change of seasons, as a few familiar 

 examples will indicate. Tubers of the earlier varieties 

 of the potato, that ripen in northern countries by the be- 

 ginning of August, do not sprout if left in the ground 

 till October, but if stored in a cellar during winter at a 

 temperature little abo^•e freezing, they often begin to 

 sprout in March. Bulbs of the crocus, tulip, narcissus, 

 crown imperial etc. , that form in spring, lie dormant in 

 the warm soil during summer and early autumn, but start 

 vigorously in the colder soil of the late autumn or the 

 succeeding spring. The buds of many trees, that form 

 in summer for the next year's foliage and flowers, remain 

 dormant during the hot weather of August and Septem- 



