RELATIONS OP BOTANY TO AGRICULTURE. 427 



the simplest plants this division occurs within the outer envelope, 

 and each portion develops upon itself a new membrane and grad- 

 ually increases to the usual size of the parent. By this process, 

 the original cell is burst and destroyed, and the same operation 

 continues during- the growing period, producing in the aggregate 

 countless numbers of individuals. Most plants, however, consist 

 of a combination of cells, arranged in threads, or thin expansions, 

 or masses of various but definite forms, each species assuming at 

 length, on maturity, its own characteristic shape and substance. 



Ordinary growth, as in the grasses, occurs by the subdivision 

 of cells into two parts by the formation of a partition in the proto- 

 plasm, and then each of these parts enlarges to the normal size 

 and becomes a perfect cell. The lower or inner one generally 

 remains stationary, while the upper or outer one again subdivides, 

 and so the process goes on until the plant attains its complete 

 development. This growth may be well nigh imperceptible, as in 

 some of the lichens, which stand for centuries almost unchanged, 

 or it may be amazingly rapid, as in the giant puff-ball, which has 

 been known to form sixty-six millions of cells per minute. Upon 

 reaching a certain degree of maturity, every species is observed 

 to produce and cast off seeds, bulblets, or spores, usually in large 

 numbers, for the continuation of its kind. This may be followed 

 by immediate death and decay, as in the mushroom and century- 

 plant, or, as in most perennials, growth and fruiting may go on 

 together for many years, and the decline of the vital force be 

 gradual. In the simpler forms of vegetation we find great uni- 

 formity of structure, even when the individual attains an enormous 

 size, as in the gigautic kelp of Cape Horn, which reaches a length 

 of several hundred feet, but shows no distinction of vegetative 

 organs. If, however, we plant the seed of an apple, and watch 

 its progress from germination to maturity, we notice at once sev- 

 eral sets of organs with distinct forms and functions. The young 

 tree has a root which avoids the light and penetrates the soil in 

 all directions where the conditions are suitable. It has a stem of 

 curious construction which rises from the ground, lifting its head 

 high into the air. It is covered with leaves, which are evidently 

 designed to expose the largest possible surface to the sunlight 

 and the, atmosphere. After a few years of growth, a portion of 

 its annual crop of buds develop into blossoms, which in time 

 become fruits with seeds. 



Thus the chief end of all vegetable life, so far as the plant itself 



