PROCESS OF PLANT GROWTH. 53 



They bear about the same relation to it that a Webster's 

 spelling-book does to English literature. The word botany- 

 means a plant, and every plant has once existed in a single 

 cell. All plants are either single cells or aggregations of 

 them, and differ from each other only in the number, fonn 

 and mode of comljination of these their constituent elements. 

 The foundation of our science, therefore, is seen to lie in a 

 knowledffe of the vesfetable cell and the changes of which it is 

 susceptible. By the aid of the compound microscope we learn 

 that a uni-cellular plant consists of a globule of protoplasm 

 enveloped in a thin membrane of cellulose. This protoplasm 

 is in an albuminous fluid, somewhat like the white of an Qgg, 

 and usuall}^ containing one or more granules floating in it, 

 which are apparently analogous to the yolk. Under the influ- 

 ence of the mysterious force which we call life, this gelatinous 

 fluid exhibits a tendency, under favoring circumstances, to 

 divide and increase in quantit}', producing the phenomenon of 

 growth. In the simplest plants this division occurs within the 

 outer envelope, and each portion develops upon itself a new 

 membrane and o-raduallv increases to the usual size of the 

 parent. By tliis process, the original cell is burst and de- 

 stroyed, and the same operation continues during the growing 

 period, producing in the aggregate countless numbers of indi- 

 viduals. 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. 



Ordinarv sfi'owth, as in the Grasses, occurs by the subdivision 

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

 toplasm, and then each of these parts enlarges to the normal 

 size and becomes a perfect cell. The lower or inner one gen- 

 erally 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 cen- 

 turies almost unchanged, or it may be amazingly rapid, as in 

 the giant pufi'-ball, which has been kno^vn to form sixtj'^-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 



