LESSONS IN BOTANY. 193 



in a saucer with a little water it will spread out in good shape 

 for study. Then notice the form and color of the hairlike fila- 

 ments and possibly careful observation will allow one to see the 

 slow vibratory movements which give this plant the name of 

 Oscillaria. The filaments are composed of cells attached end to 

 end in colonies, but each is an individual as fully as the cells of 

 protococcus. 



These minute plants all live in water or in damp shady places, 

 yet all retain their vitality for a long time when dried so as to 

 form an impalpable dust. While these plants are minute in size 

 and simple in structure they constitute an important branch of 

 the vegetable kingdom. 



On the surface of stagnant water and in quiet water along the 

 edges of streams, in the early spring, little patches of a frothy 

 substance appears, sometimes called frog spittle, later the sur- 

 face is covered with a bright green scum, and during June and 

 July great patches of a dirty brownish scum is present with the 

 green. When lifted from the water it has a slippery feel, and 

 strings out like wet hair. The plant is some species of Spirogyra 

 or Zygnema. It may be grown for observation in an open dish 

 of water, with some soil at the bottom, in which some water lov- 

 ing plant is growing. 



The long hairlike filaments are colonies of cells attached end 

 to end as in oscillaria. The cells in spirogyra are marked by 

 spiral bands of chlorophyll, while in zygnema there is a central 

 starlike nucleus, with the chlorophyll in bands or plates. They 

 multiply by division as do protococcus and oscillaria, but in ad- 

 dition there is another form of reproduction. At the close of their 

 growth in the spring, the cells push out little processes from 

 their sides, which meet similar processes from other cells of par- 

 allel filaments. They flatten upon each other, the walls fuse and 

 are absorbed, leaving a connecting channel between the two cells, 

 through which the protoplasm of both cells become one mass. 

 This mass secretes a wall of cellulose forming a zygospore or 

 germ, which has much thicker walls than the ordinary cell, and 

 from which a colony of cells or plants may be developed. 

 L. S.-43 



