THE CELL. 



81 



the protoplasm in each cell contracts, 

 that in one cell graduall)' passes over 

 to the other, r.nd the two masses unite 

 into one, forming a. new cell or spore 

 (Fig. 180, 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 ia 

 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 

 (I, 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-formation by conjugation in Spirogyra: I, 3, j, 4, the successive 

 stage?. Fig. 187. Free cell-formation in the asci of a Lichen ^Cladonia). 



6 



