148 STUDY OF COMMON PLANTS. 



the group to which they belong, and it is often possible to 

 determine not only genus, but species, from a single teleuto- 

 spore. The spores of many algee are merely minute masses 

 of naked protoplasm which are propelled through the water 

 by means of cilia. Others produce zygospores such as 

 those of Spirogyra, or oospores like those of Vaucheria, and 

 still other forms occur. They are adapted to the medium 

 by which they are transported, those of ferns being so light 

 that they are boi'ne by the wind hundreds of miles, and 

 those of al^se being, as already shown, provided with cilia, 

 or in other ways adapted to movement through the water. 

 Those of certain fungi are sticky, and are carried away by 

 visiting insects. Accordingly we are to think of the spore, 

 in this respect at least, as the physiological equivalent of 

 the seed. It is the plant in a transportable condition. 



Comparing the germination of spores and seeds, we find 

 the phenomena so different that we can scarcely point to 

 any features in common beyond those character- 

 ermina on, .^^.^ ^^ growth in general. In the germination 

 of a seed, the embryo already formed increases in size ; the 

 radicle is protruded; the plumule unfolds and gradually 

 forms the stem and leaves of the new plant. Spores, on 

 the contrary, having no embryo, send out a simple germ- 

 tube, as in the case of the brown moulds, or they may form 

 zoospores, which afterwards produce a mycelium, as in the 

 grape-vine mildew, or they may give rise directly to a 

 protonema or prothallium, as in the mosses and ferns, but 

 the development of a preexisting embryo is wanting, ex- 

 cept in such plants as Selaginella, which share in part this 

 feature of the flowering plants. The conditions of ger- 

 mination are the same as those required by seeds ; namely, 

 moisture, a suitable temperature, and access of oxygen. 

 Certain spores lose their capacity for germination very 



