32 ULOTHRIX. 



7. Young plants of several cells beginning to assume the 

 characteristics of their parents. 



8 . The developing ' ' holdfast . ' ' 



Make drawings illustrating the stages seen in the process 

 of reproduction. 



ANNOTATIONS. 



In the plant Ulothrix we have our first illustration 

 of a filamentous green Alga of the family Chlorophyceae. 

 Its cylindrical cells are placed end to end, and much 

 more firmly united than those of any plant we have yet 

 studied. Furthermore, in most species the basal cell 

 attaches the plant, thereby giving it a degree of perma- 

 nence of location. In each cell, excepting the "hold- 

 fast," we have a well-organized chloroplast in which 

 are special nutritive organs known as pyrenoids, which 

 are peculiar to some Algae. The plants grow in length 

 by having the cells enlarge and divide at right angles 

 to the long axis of the filament. Sometimes plants 

 break, resulting in the production of two or more new 

 individuals. 



Asexual reproduction takes place through the formation, 

 by internal division, of specialized bodies known as spores, 

 called zoospores because they move as certain small 

 animals. These zoospores may be formed in the interior 

 of any nutritive cell by the division of its protoplasm, 

 all of which is used in their formation. When the wall 

 of the mother- cell breaks, the zoospores escape and swim 

 about for a time, then come to rest on some support, 

 attach themselves at their ciliated end, and begin to grow 

 into new Ulothrix plants. Obviously this zoospore habit 



