THE PROBLEM OF SEX IN PLANTS 
35 1 
and the gemma of various species of liverworts, mosses, 
and ferns (Fig. 260). 
An interesting form of vegetative multiplication is 
illustrated by the fern W oodwardia 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; b, 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- 
