46 NORMAL HISTOLOGY. 



SPIROGYRA. 



Spirogyra is a unicellular, chlorophyl-bearing plant which repro- 

 duces by normal fission and by conjugation. 



Classification : 



Kingdom Vegetable. 

 Series Cryptogamia. 



Sub-kingdom Thallophyta. 

 Class Algas. 



Sub-class Chlorophyceae. 

 Order Conjugatales. 



Family Zygnemacese. 

 Genus Spirogyra. 



Species Spirogyra nitida. 



Spirogyra maxima. 



Life History and Morphology. Spirogyra maxima, commonly 

 called Brook Silk, consists of a cylindrical cell, longer than broad. 

 The cells, placed end to end, are united into long filaments by a 

 gelatinous secretion. They contain chlorophyl bodies arranged in 

 spiral form, hence the generic name. These are the cliromato- 

 phores, or chloroplasts. A nucleus is always present, but not easily 

 seen. Fission occurs by the normal method and may take place in 

 any cell of a filament. Eeproduction also takes place by conjuga- 

 tion i. e., two adjacent cells of filaments lying near, or in contact 

 with each other, unite by the protoplasm of one being discharged into 

 that of the other. This is accomplished by tubular projections being 

 thrown out from each cell, which meet and form a passageway be- 

 tween the cells. In this case the cells are alike and distinction of sex 

 has not yet been discovered. The new cell produced by the conju- 

 gation is called a zygospore. The encysted zygospore becomes em- 

 bedded in the mud and preserves the life of the plant through the 

 winter. If develops into a new plant by the protrusion of the in- 

 ner coat through the broken outer coat, when fission takes place, and 

 a filament is produced by the vegetative process. By some, spirogyra 

 is supposed to illustrate sexual reproduction, the conjugating cells 

 being the gametes and producing by their union the zygospores. The 

 sexual character of the cells may yet be proven, for there may be 



