SECTION 16.] STRUCTURE AND GROWTH. 129 



1. ANATOMICAL STRUCTURE AND GROWTH. 



394. Growth is the increase of a living thing in size and substance* It 

 appears so natural that plants and animals should grow, that one rarely 

 thinks of it as requiring explanation. It seems enough to say that a thing 

 is so because it grew so. Growth from the seed, the germination and de- 

 velopment of an embryo into a plantlet, and at length into a mature plant 

 (as illustrated in Sections II. and III.), can be followed by ordinary obser- 

 vation. But the embryo is already a miniature plantlet, sometimes with 

 hardly any visible distinction of parts, but often one which has already 

 made very considerable growth in the seed. To investigate the formation 

 and growth of the embryo itself requires well-trained eyes and hands, and 

 the expert use of a good compound microscope. So this is beyond the 

 reach of a beginner. 



395. Moreover, although observation may show that a seedling, weigh- 

 ing only two or three grains, may double its bulk and weight every week 

 of its early growth, and may in time produce a huge amount of vegetable 

 matter, it is still to be asked what this vegetable matter is, where it came 

 from, and by what means plants are able to increase and accumulate it, and 

 build it up into the fabric of herbs and shrubs and lofty trees. 



396. Protoplasm. All this fabric was built up under life, but only a 

 small portion of it is at any one time alive. As growth proceeds, life is 

 passed on from the old to the new parts, much as it has passed on from 

 parent to offspring, from generation to generation in unbroken continuity. 

 Protoplasm is the common name of that plant-stuff in which life essentially 

 resides. All growth depends upon it; for it has the peculiar power of 

 growing and multiplying and building up a living structure, the animal 

 MO less than the vegetable structure, for it is essentially the same in both. 

 Indeed, all the animal protoplasm comes primarily from the vegetable, 

 which has the prerogative of producing it ; and the protoplasm of plants 

 furnishes all that portion of the food of animals which forms their flesh 

 and living fabric. 



397- The very simplest plants (if such may specifically be called plants 

 rather than animals, or one may say, the simplest living things) are mere 

 particles, or pellets, or threads, or even' indefinite masses of protoplasm of 

 vague form, which possess powers of motion or of changing their shape, 

 of imbibing water, air, and even other matters, and of assimilating these 

 into plant-stuff for their own growth and multiplication. Their growth 

 is increase in substance by incorporation of that which they take in and 

 assimilate. Their multiplication is by spontaneous division of their sub- 

 stance or body into two or more, each capable of continuing the process. 



398. The embryo of a phanerogamous plant at its beginning (344) is es- 

 sentially such a globule of protoplasm, which soon constricts itself into two 

 and more such globules, which hold together inseparably in a row ; then 

 the last of the row divides without separation in the two other planes, tc 



