LONGEVITY OF PLANTS. 661 



accommodate itself to the change, and must thereby, directly or indi- 

 rectly, suffer a modification in the length and kind of its life. The 

 soil also, and changes in its condition, have their influence, and sur- 

 rounding plants and animals have their effects, all of which the plant 

 may feel and show very plainly. 



Evidence that the causes which we have only briefly touched upon 

 here play a part in determining the duration of the life of different 

 plants is afforded by cultivation and by the geographical distribution 

 of species. It is well known that when plants are taken into cultiva- 

 tion, and exposed to different temperatures, different degrees of moist- 

 ure, and different soils from those they have been accustomed to, and 

 direct attacks are made upon their growth, they often suffer changes 

 of one kind or another, and the duration of their life especially is 

 affected. Modifications of external influences may be brought about 

 partly by sowing the seed at different seasons from the usual one, 

 partly by artificial stimulation, pruning, manuring, withholding moist- 

 ure, etc. The object in these processes has generally been to make 

 the plant go through its course faster, so as to secure an earlier bloom- 

 ing or fruiting ; and its life has been shortened without that being the 

 real intention. The other object, of prolonging the life, is also desir- 

 able ; and there are numerous examples in which the life of plants may 

 be lengthened or shortened by different modes of cultivation. 



Particularly interesting examples of the evolution of different 

 life-terms are exhibited in the geographical distribution of plants. If 

 we consider the whole earth as to its climate, we shall observe that in 

 a few regions near the equator, that have a uniform climate, plants 

 will grow all the year through without manifesting any periodical 

 preferences. This is the case, for example, east of the Andes in 

 Northern Brazil, in Guiana, and in Java, where the vegetation is 

 green and blooms continuously, where most species become woody, 

 and nearly all live long and bear fruit often ; while the short-lived, 

 once-fruiting species retire to the background. In other tropical re- 

 gions, where a periodical climate is produced by differences in the 

 moisture of the atmosphere, the long-lived plants prevail, and the 

 ground is so occupied with them till the coming on of the dry season 

 that the short-lived kinds can not find room upon it. The case is dif- 

 ferent in those regions where spots become barren of vegetation in 

 consequence of the parching heat. Then, when the rainy season sets 

 in, the annuals quickly spring up between the bulbous and tuberous 

 herbs that are able to keep their places through the drought. The 

 short-lived species are of most importance where a warm season alter- 

 nates with a cold one, and the warm season lasts long enough for them 

 to go within its term through the whole cycle of their life, from their 

 seed-time to the ripening of their fruit. As the warm season becomes 

 shorter the number of annuals is reduced, until finally, when the sum- 

 mer is not long enough for any of them to perfect their seed, they 



