THE CELL. 



81 



186 



the protoplasm iu each cell contracts, 

 that in one cell gradually passes over 

 to the other, and the two masses unite 

 into one, forming a new cell or spore 

 (Fig. 186, sp). A cell-wall is secreted, 

 and the spore, after some length of 

 time, begins to grow, and another 

 plant like the adult form is the result. 

 104. Free cell-formation is ex- 

 hibited in the production of spores in 

 some Fungi, Lichens, in the embryo- 

 sac of the flowering plants, etc. New 

 centres of formation arise in the mass, 

 and around each of these a portion of 

 the protoplasm collects and forms a 

 new cell (Fig. 187) ; only a part of 

 the protoplasm is consumed, a portion remaining over. 

 One or many cells may thus arise in any cell. A fourth 

 method of cell-formation is by division. Here the pro- 

 toplasm separates into two masses, a partition wall is 

 secreted which separates the two portions, and thus two new 

 cells are formed. Recent investigations of Strasburger show 

 that the process, when a nucleus is present, is very com- 

 plicated. It is illustrated in Fig. 188, 

 which represents the successive stages 

 (J, II, III, IV, V, VI) in the forma- 

 tion of spores (in Psilotum triquetrurn). 

 The nucleus appears filamentous in 

 structure, and the' threads arrange 

 themselves approximately parallel to 



Fig. 186. Cell-formatiun by conjugation in Spirogyra; I, 2, 3, 4, the successive 

 stages. Fig. 187. Free cell-formation in tlie aiaci of a Lichen (C/ff^i^KzVz). 



6 



