THE PROBXEM OF SEX IN PLANTS 351 



and the gemma of various species of liverworts, mosses, 

 and ferns (Fig. 260). 



An interesting form of vegetative multiplication is 

 illustrated by the fern Woodwardia orientalis, where 

 new plantlets arise at numerous points on the upper 

 surface of the leaves (Fig. 261). The number of in- 

 dividuals is thereby increased or multiplied, hence the 

 term vegetative multiplication. 



FIG. 260. Hymenophyllum sp. Prothallus. a, antheridia; 6, arche- 

 gonia; g, gemmae. (After Winifred J. Robinson.) 



318. Reproduction by Spores. In many plants such, 

 for example, as the fern, the parent plant, while retaining 

 its own vegetative organs intact, gives off individual 

 cells (the spores), which become the starting points of 

 new individuals. The most distinctive thing about a spore 

 is that it escapes, or becomes separated from the parent, while 

 all the other cells remain organically united. 



In some one-celled plants (e.g., yeast, Fig. 67), the en- 

 tire plant body (except the cell-wall) may become organ- 



