CELL-FORMATION. 35 



protoplasm, and by no portion of the cell-wall of the 

 parent-cell being used by the new or daughter-cells. The 

 following are the most important methods. 



Division. — When the nucleus of a mother-cell disappears 

 and four nuclei appear, round these nuclei the whole of the 

 protoplasm accumulates, forming four new cells, each of 

 which secretes its own cell-wall, the cell-wall of the mother- 

 cell then disappears, and the daughter-cells are free. In this 

 way are formed the spores of mosses and the higher Crypto- 

 gams and the pollen grains of flowering plants. In other 

 cases, as in many seaweeds and fungi, the protoplasm 

 becomes divided into several daughter-cells, which escape 

 from the mother-cell as primordial cells, and exhibit spon- 

 taneous movements due to the presence of cilia.. Such 

 cells, if possessed of sexual functions, either always remain 

 naked or without a cell-wall, or after moving about for 

 some time the cilia contract and a cell-wall is secreted. 



Free-cell Formation. — A portion of the protoplasm of a 

 mother-cell become rounded and form cells which form 

 walls of their own ; the rest of the protoplasm remains in 

 the mother-cell, which Hves for some time after the change. 

 The spores of some groups of fungi and certain cells in the 

 young seeds of flowering plants are formed in this way. 



Conjugation. — The protoplasm of two cells, usually 

 belonging to distinct individuals, unite together to form 

 one cell which secretes a thick cell-wall, and is known as a 

 zygospore. Zygospores are always reproductive cells, and 

 as they do not grow into a new individual at once, but 

 remain during the winter in a passive condition, protected 

 by the very thick, usually warted or spinulose cell-wall, are 

 known as resting-spores. The fact of two cells belonging to 

 distinct individuals of the same species becoming blended 



