98 PRACTICAL BOTANY. 



bodies tire scattered quite regularly over the entire sur- 

 face of the cell. In others they collect into two somewhat 

 starlike masses connected by a narrow band, giving a 

 shape resembling a dumb-bell. In others they collect into 

 spiral bands. The last forms are known as Spirogyra, 

 of which there are many varieties. 



The asexual reproduction is by the transverse fission of 

 the cells. It is the usual process of the division of the 

 protoplasm and the formation of a cellulose wall across the 

 cell. The division takes place in the dark. It is best 

 observed by keeping the plants in a totally dark place for 

 some hours and then examining at once. This mode of 

 reproduction accounts for the long unbranched filaments. 



The sexual reproduction may be seen at various seasons, 

 but is more likely to be met with in spring or in summer. 

 When the plant is at this stage, it takes on a brownish 

 color. The male and female filaments cannot be distin- 

 guished from each other, even under the microscope, but 

 when two filaments of opposite sexes happen to be in 

 proximity to each other, projections develop on the adja- 

 cent cell walls until they meet. (Fig 57, J?.) The cell 

 walls break away at the junction, and the contents of the 

 male cell are emptied into the other cell. A zygospore is 

 thus produced that becomes encysted and falls to the bot- 

 tom of the water, where, imbedded in the mud, it pre- 

 serves the life of the plant until the next season. On the 

 return of spring the zygospore grows in the asexual way 

 into a new filament. This is gonidial reproduction. 



SPIROGYRA. PRACTICAL STUDIES. 



1. Observe the light green color of the plant when seen 

 in mass. Notice that most species are slippery to the touch. 

 Place a little in water on a glass slip, hold the slip over a 

 white surface, and notice that the plants form fine uri- 



