244 GENERAL MORPHOLOGY OF PLANTS 



It grows in length by the repeated division of certain cells, the 

 marks of the successive divisions remaining on the cell wall near 

 one end, giving a peculiar appearance as in fig. 186. In asexual 

 reproduction the content of a cell forms a single large zoospore or 

 swimming spore, with a crown of cilia near one end. After 

 escaping from the parent cell and swimming around it comes to 

 rest, attaches itself to a place of support by a disk-like grappler, 

 and grows into another (Edogonium thread. In sexual repro- 

 duction certain cells become transformed into female organs by 

 becoming enlarged and rounded. This enlarged cell is the egg 

 case (oogonium, or egg producer), and contains a single large 

 egg (or oospore). Other cells become divided into smaller cells 



by cross walls. Each of these small cells 

 Sporophyte , .. . . 



is a male organ, the sperm case (anthe- 



^ium); The sperms are like the swim- 

 ming spores, but much smaller and devoid 

 of chlorophyll. One enters an egg case, 

 j\ passes into the egg and unites with the 

 nucleus. The fertilized egg (oospore) then 

 acquires a thick wall and becomes a rest- 

 ing spore. After a period of rest the pro- 

 toplasm of the fertilized egg forms four 

 Diagram NO. ii. nius- zoospores, each of which can grow into an 



trating the life cycle in the 



development of (Edogonium. (Edogonium plant, thus completing the life 



Course of development fol- 

 lows the direction indicated cycle. In some species both the sperm 



by arrows. Ayrote equals 



fertilized egg. Asexual mui- case an d egg case are on the same thread, 



tiphcation by asexual spores. 



while in other species they are on separate 



threads. In still others small male plants are first formed from 

 a special swimming spore intermediate in size and color between 

 a zoospore and sperm. 



379. Coleochaete. Coleochcete represents the highest stage 

 of development of the filamentous green algae. The plants 

 occur in fresh water attached to larger aquatic plants. They 

 are mostly filamentous and branched, but a few form small, 

 flattened, more or less circular cell plates. Asexual repro- 

 duction is by biciliate zoospores, one each from a parent cell. 



