142 



BOTANY. 



reproduction. In the plants under consideration there is 

 barely enough coherence of the cells to enable them to 



constitute a plant-body, and one 

 can readily see that the same fis- 

 sion of the cells which here in- 

 creases the size of the plant 

 would, if the cells cohered less, 

 simply increase the number of 



252. As might be expected. 



Fig. 73.— a, beginning of the sexual reproduction of a pond-scum (Spir- 

 ogyra longata) ; a, beginning of the formation of lateral tubes ; b, c, the 

 tubes in contact. B, the protoplasm passing from one cell to the other at 

 a ; 6, the mass of protoplasm formed by the union of the protoplasmic con- 

 tents of the two cells. C, two young resting spores (c) , each with a cell- 

 wall. They contain numerous oil-drops, and are still enclosed by the 

 walls of the parent cell. Magnified 550 times. 



the filaments occasionally separate spontaneously into sev- 

 eral parts of a considerable length, and the parts floating 

 away give rise to new filaments. The separation takes 

 place by the cells first rounding ofE slightly at the ends, so 

 that theil union is weakened at their corners ; finally, only 

 the centres of the rounded ends are left in slight contact, 

 which soon breaks. 



