LONGEVITY OF PLANTS. 659 



of the parts can be perceived. Food is taken in on all sides alike, and 

 is worked up in the whole plasma of the cell and applied to the growth 

 of the cell-body, to the multiplication of cells by division, or is stored 

 up as reserve food. This is possible because the cell either lives con- 

 tinuously in a uniform element, water, or, if it dries up, simply sus- 

 pends its life while the dryness continues. The simplest structure, a 

 uniform medium, the most speedy performance of the functions of life, 

 and the shortest life-term, thus go together. Now, take a plant which 

 no longer consists of a single cell, but is a structure of a larger or 

 smaller number of different cells, which no longer lives in a uniform, 

 constant element, but has its body partly in the ground and partly in 

 the air, so that it is exposed to all the changes to which those elements 

 are subject. In this case a complete differentiation of the organs for 

 different life-functions, of which there is no need in the one-celled 

 plant, becomes essential. There must be a root to take up fluid food ; 

 leaves to absorb gaseous matters and elaborate them under the influence 

 of light into new substances to be applied to the growth and strength- 

 ening of the plant or to be stored up in particular parts as reserve 

 food ; and, besides, particular organs, distinct from the food-organs, 

 for propagation, of the most complicated character, such as are not 

 needed in water-plants, where cross-fertilization, so difficult to secure in 

 the free air, is easily and directly effected. Furthermore, since plants 

 rooted in the ground can not move about, the advantage which change 

 of place offers to the extension of the species is compensated for by 

 the seeds and fruits being endowed with peculiar arrangements by 

 means of which they can spread their kind through a wider circle. 



Evidently, all these organs can not be formed in a few days, but a 

 considerable time is needed to bring their development and the fruit- 

 ing process to perfection. Additional complications now enter into 

 the life-relations of the plant. While the fruit-organs perish, when 

 they are separated from the stem at maturity, the life of the plant it- 

 self does not necessarily cease when they are dropped, but has a possi- 

 bility of continuance dependent on a variety of conditions, the chief 

 of which is, whether the other organs have been exhausted or not. 



The prolongation of life is also affected by a great number of outer 

 conditions. The plant has to be subjected to the changes of the sea- 

 sons ; it has to struggle for support in competition with other plants ; 

 it has to deal with animals, some of which are beneficial, some damag- 

 ing to it ; and it may or may not find a sufficiency of food in the soil 

 in which it is trying to grow. With respect to all its external rela- 

 tions, it must have the faculty of adapting itself, by extending its 

 organs in one or another direction. And this adaptation is complicated 

 by the fact that it has to be modified to meet different conditions, at 

 different stages of development, and that the plant can flourish only 

 when all its stages of growth are simultaneous with favoring outward 

 circumstances, and can be completed while these continue. 



