270 COLLEGE BOTANY 



lar filaments. There is no non-sexual reproduction other than 

 simple cell division and no motile cells. Sexual reproduction is by 

 conjugation of the protoplasts, usually tlirough conjugating tube 

 stnictures. Desmids and Spirogyra axe the most common forms. 



Spirogyra (Fig. 122, a^b) is a multicellular, filajnentous 

 plant characterized by the very prominent spiral, band-like 

 chloroplasts. Each cell is uninuclear and capable of division. In 

 the sexual reproduction small tubes are formed from the cells 

 of two adjacent filaments which finally meet and fuse (conju- 

 gation) . The 'contents of the cells of one tube pass into 

 the cells of the other and the result is the formation of large 

 resting spores, known as zygospores. Sometimes cells resem- 

 bling zygospores are formed without conjugation; this process 

 is known as parthenogenesis. 



Desmids is a term used to designate a great niunber of 

 minute, unicellular floating fresh-water plants of great beauty. 

 The cell is organized into symmetrical halves and the reproduc- 

 tion is the same as in the Spirogyra. 



The Phwophycece or brovra algse are confined to the salt 

 waters and are most abundant in relatively cold regions. Many 

 of them are very large, and in fact the longest known plants 

 belong to this group. They are especially abundant on our 

 Pacific Coast and include the kelps and O'ther large forms. They 

 have been used to some extent as a source of potassium for fer- 

 tilizers. They are well worthy of an extensive discussion, which 

 cannot be given in a book of this kind. 



The Rhodophycew or red algse are mostly salt-water forms 

 and are most abundant in the warm waters. They range from 

 very small forms to species of considerable size, but are not 

 nearly so large as the brown algse. Some of them are very com- 

 plex in structure and method of reproduction and are of consid- 

 erable importance in the study of the evolution of plant life. 

 Some few of the gelatino'us species are of value as foods. 



Anomalous Algce. — There are two groups of algse that do' 

 not appear to fit into any of the recognized groups. They are 

 the Diatoms and the Stoneworts. 



