352 STRUCTURE AND LIFE HISTORIES 
ized inty spores, which escape from the cell-wall of the 
mother-cell. In a number of many-celled plants (e.g., 
Ulothrix) practically every protoplast has the capacity of 
becoming organized into one or more spores which escape 
from the old cell-cavity. The next higher step is the 
restriction of spore formation to certain cells in special 
organs (sporangia), while the other cells function only 
vegetatively. 
FIG. 261. Woodwardia orientalis. Portion of a leaf bearing numerous 
young plantlets on its upper surface. 
319. Cell-fusions. Through all the variations of re- 
production by spores there is, as a rule, only the separation 
of protoplasts from the parent body, never a cell-fusion or 
nuclear-fusion. Some plants, however, such as Ulothrix 
(Fig. 262), have been found to produce two sizes of 
spores, and the small spores must always unite before 
they can develop into full-sized, mature individuals. 1 
Attention has already been called (Chapter XVIII) to 
the condition of similar sized gametes (isogamy), as in 
Spirogyra, in contrast to that of unequal gametes (hetero- 
gamy), as in Ascophyllum and Fucus. 
1 In certain cases (e.g., Ulothrix) the microspores may develop small, 
imperfect individuals without fusion. 
