22 



ELEMENTARY STUDIES IN BOTANY 



for spores of the Red Algge, for example, have no cilia (Fig. 

 17) and are carried about passively by the water, while the 

 .spores of higher plants are carried through the air. Nor 

 must it be supposed that spores are necessarily produced 

 by the division of a protoplast; they generally are, but 

 sometimes the whole protoplast escapes from its investing 

 wall and is a spore (Fig. 15, A). Nor is a spore always 

 naked (without a wall). Although swimming spores are 



usually naked, spores exposed 

 to the air have walls, and 

 sometimes very heavy walls. 

 A spore is recognized, there- 

 fore, not by its cilia, its form, 

 its covering, or its origin, but 

 simply from the fact that it 

 is able to produce a new 

 plant. The process by which 

 a spore starts a new plant is 

 called germination, so that 

 the business of a spore is to 

 germinate. 



In most of the Alga3, 

 spores are produced by the 

 ordinary vegetative cells, that is, by cells that are a part of the 

 vegetative body and form spores only when the conditions 

 for vegetative work become unfavorable. Gradually, among 

 the Alga3, however, the cell that produces spores becomes 

 more and more distinct from the other cells, until finally 

 it is entirely distinct, doing no vegetative work, and only 

 producing spores, as in the brown alga shown in Fig. 16 

 and in the red alga shown in Fig. 17. Such a cell is called 

 a sporangium, which means " spore-case." Although Alga3 

 are characterized by an abundant formation of spores, it 

 is only among the higher groups of Algae that sporangia 

 become differentiated from the rest of the body. 



FIG. 17. Portion of a red seaweed, show- 

 ing a sporangium with its four spores 

 (A), and another one (B) from which 

 the spores (with no cilia) have escaped. 



