222 PHYSIOGRAPHY. [chap. 



cell (the embryo cell) contained within the ovule, while its 

 conclusion is the production of new embryo cells, every one 

 of which may become competent to repeat the whole series. 

 Each term of the series is a stage of what is called the de- 

 velopment of the plant ; and, if successive stages of this 

 development are compared, it will be found that the plant 

 becomes more complex the further its development ad- 

 vances. The embryo plant, in the pea, is a more complex 

 structure than the embryo cell in the ovule ; the blossoming 

 plant is more complex than the young plant before flowering; 

 and this increase of complexity is true, not only of the out- 

 wardly visible ])arts, but of the inward structure, of the grow- 

 ing plant. Nevertheless, it is to be observed, that the full- 

 grown plant is as much an aggregate of nucleated cells, more 

 or less modified, as is the embryo ; and every change in the 

 form and size of the growing plant is, simply, the expression 

 of the mode of growth and multiplication of the individual 

 cells of which the body of the plant is made up. 



The process of evolution, from an extremely simple to a 

 highly complex condition, thus exemplified by the pea-plant, 

 is characteristic of living matter. For, although there is a 

 superficial similarity between the growth of a plant and the 

 tree-like form which some bodies assume in the act of crys- 

 tallisation, as is well exemplified by the hoar-frost on a 

 window-pane ; yet, a very slight examination shows that the 

 two processes are, in reality, altogether different. When an 

 individual crystal grows, the new matter is added upon its 

 exterior ; and when crystalline bodies assume an arborescent 

 form, the first crystal that is deposited does not grow into 

 the crystal tree, but new crystals are added to the outside of 

 the first, in such a manner, that the compound mass has a 

 tree-like shape. . But, when the embryo-cell grows, the addi- 

 tion of matter takes place within its own substance, just as a 



