OTHER ALGM 171 



two-and-two by means of short tubes, the one plant being male 

 and the other female. The tubes are outgrowths from both 

 plants which tend to unite ; the separating walls are dissolved 

 and the contents of the male cells pass into and unite with the 

 contents of the female cells, forming what is known as zygo- 

 spores, which will eventually i)roduce new plants. 



Ulothrix is another filamentous form which produces a 

 large number of ciliated free-swimming cells known as 

 zoospores. They swim for a time, come to rest and each grows 

 into a new plant. In some cases these free-swimming cells 

 (gametes) unite in pairs and form zygospores. 



CEdogonium (Fig. 110) is another filamentous form, a spe- 

 cies which presents a great variation in sexual character. A 

 cell may produce a single large, ciliated cell or zoospore which 

 will swim for a time, attach itself and grow into a new plant. 

 Or, it may produce a large female cell (gamete) w^iicli is 

 retained in the old cell-wall (oogonium) and fertilized by small 

 free-swimming zoospores or sperms (gametes) which are pro- 

 duced by another cell or antheridium. In other species of 

 G^dogonium the oogonia are produced in large female plants and 

 the antheridia in the small male plants. 



The Vaucheria are filamentous but unicellular and multi- 

 nuclear forms. The non-sexual reproduction is by the formation 

 of a cross wall at the end of a filament, thus forming a cell from 

 which a single large motile or non-motile spore is produced. The 

 sexual reprodiiction is by the formation of oval oogonia, each 

 containing a single large ovum or egg and curved, tubular an- 

 theridium containing many small sperms. The sperm escape 

 and at last one reaches the ovum which is fertilized and results 

 in an oospore or resting spore. This is more nearly like tlie 

 liverworts, mosses and ferns than most of the alga?. 



Other Algae. — Concerning the many other forms of algrp, 

 wo may briefly say that they are the forests and the i)astiires of 



