106 STUDY OF COMMON PLANTS. 



their peculiarities are worth taking pains to secure. Stras- 

 burger recommends ^ that vigorous specimens of Vaucheria, 

 growing in running water, be obtained the day before, 

 placed in shallow vessels, and fresh water poured over 

 them. The swarm-spores are formed the following morn- 

 ing, and, on account of their large size, both their structure 

 and development are readily observed. 



No further special directions will be needed beyond 

 those in the manuals referred to, which should be care- 

 fully read. As complete a study as possible should be 

 made of this plant, since it stands as a representative of 

 those algse in which the sexual reproduction has proceeded 

 a step farther than in Spirogyra, male and female cells 

 being distinctly differentiated. Many of these are also 

 reproduced by swarm-spores. These two modes of repro- 

 duction are so common that we expect, as a general rule, 

 to find the algse reproducing themselves both sexually and 

 non-sexuallj', a fact that continually presents itself in 

 studying other groups of plants, but not often in quite so 

 striking a way as here. The non-sexual process is a means 

 of rapid reproduction ; sexual reproduction, on the other 

 hand, commonly results, in the lower plants at least, in the 

 formation of a resting-spore by which the plant is carried 

 through various vicissitudes and dangers, and in which 

 by a mingling of the male and female elements in the 

 process of fertilization, certain other advantages, not yet 

 fully ^^nderstood, are attained. 



The brown and red algse grow in salt water in nearly all 

 cases, and are seaweeds properly so called. They present 

 many forms no less interesting than the green algse, but as 

 they will not be accessible to the great majority of those 



' Practical Botany, p. 250. 



