The Orderly Cycles Pursued in Growth 367 



more difficult for them to transfer a sufficiency of water and min- 

 erals to their more distant parts, whose vitality is thus checked. 

 At the same time the increasing exposure of parts to the winds, 

 and the greater leverage thus given, leads to breakage, and hence 

 the admission of rot-producing fungi, which sooner or later bring 

 the loftiest tree to the ground. Thus trees, though they grow very 

 large, never really stop growing in size; and, moreover, they never 

 grow old in the sense that animals do, but come to their end while 

 their individual parts are still in full vigor. 



Such is the cycle of growth in the most highly organized plants, 

 and very different it is, as the reader will have noticed, from the 

 cycle displayed in the highest of animals. For animals construct 

 but a single set of organs, which last without renewal through life; 

 and when these have each grown to full size the growth of the 

 individual is stopped, though it may live for a very long period 

 thereafter. Inside of these organs the protoplasm goes on working 

 without chance for rejuvenescence, and therefore gradually wears 

 out and dies, thus fixing an internal limit to the length of the 

 animal's hfe. 



Through such a complex though orderly cycle do the most 

 highly organized plants all swing in the course of their develop- 

 ment and growth. In tropical climates the cycle is accomplished 

 without pause, except for a brief time during dissemination, but 

 in temperate regions the continuity is rudely disturbed every 

 year by the advent of winter, to which all vegetation must in 

 some way make adjustment. One could hardly believe, a priori, 

 that plants could accommodate themselves to ranges of tempera- 

 ture from forty degrees below zero to a hundred and twenty 

 above it; — yet such is the fact. This adjustment of vegetation to 

 winter introduces a secondary seasonal cycle, which has the four 

 following stages : 



The Winter is the season of dormance, in which vitahty is sus- 

 pended. The protoplasm, giving up the most of its water, ceases 

 to move, becomes hard, reduces all activities to a minimum, and 



