172 BOARD OF AGRICULTURE. 



granules of chlorophyl. The contents of each cell exhibit a 

 motion in one or more currents around and within its mem- 

 branous wall, and in the case of adjoining cells, the currents 

 usually move in opposite directions on opposite sides of the 

 intervening partition. In the protoplasm of hairs there is 

 often less freedom of motion from an apparent lack of fluid- 

 ity, and the currents appear to move to and from the nucleus 

 which lies against the cell wall. This kind of motion is 

 called rotation, and seems to result from an inherent vital 

 property of protoplasm. It is thought to occur in all cells 

 during some period of their growth. 



The so-called zoSspores, or motile germs, of some algoB 

 consist of a globule of protoplasm furnished with two or 

 more delicate arms or cilia, which revolve continually in the 

 water for an hour or more after being ejected from the parent 

 cell, and appear as if endowed with the animal power of 

 voluntary locomotion. Soon, hoAAjever, the protoplasm be- 

 gins to lose its mobility, settles quietly to the bottom, de- 

 velops upon itself an enclosing membrane, and becomes a 

 complete plant. 



There are two principal modes in which cell multiplication 

 is effected ; but in all cases it originates in the protoplasm or 

 vital fluid. In simple cellular plants it is common for the 

 protoplasm to gather itself into two or more portions within 

 the parent cell, and develop a nucleus and membrane for 

 each. These young cells then grow by the assimilation of 

 food, burst or absorb the membrane of the original cell, and 

 become independent plants. 



In the growing cells of all our higher plants a very differ- 

 ent process is observed. ^ The protoplasm flrst begins to con- 

 tract in the central portion of the cell, and either divides the 

 nucleus, or develops a new one for the cell about to be 

 formed. Each portion then secretes a new membranous 

 covering, and enlarges it by an inexplicable method called 

 intussusception of molecules, and the newer cell then re- 

 peats the process, while the older one, haying attained its 

 normal size,, remains m statu quo. Thus the plant goes 

 on increasing in all directions, Avherevcr the necessary condi- 

 tions are supplied, until it reaches maturity. Annual and 

 herbaceous plants do this in one season, biennials in two, and 



