724 



SYSTEMATIC BOTANY. 



Fig. 1096. 



rounded by a gelatinous investment, the cells exhibiting more or 

 less regular geometrical outlines and enclosed by a membrane, 

 striatefl {fig. 1096) or granular, either simply tough and con- 

 tinuous {fig. 1097), or 

 impregnated with silex 

 and separable into valves 

 {fig. 1096). Reproduc- 

 tion by spores formed 

 after conjugation of the 

 cells ifig. 1097), by zoo- 

 spores formed from the 

 cell contents, and by divi- 

 sion." The Diatomacese 

 are again divided into two 

 sections : 1. Diatomeee 

 {fig. 1096). Natives of 

 fresh or salt water, of a 

 brownish colour, valvuLir, 

 and invested by a siliceous membrane. Examjjlcs : — Diatoma, 

 Navicula. 2. BesmkUecs {fig. 1097). Found only in fresh water, 

 of a green colour, continuous, containing starch, and not in- 

 vested by a siliceous membrane. Examples: — Closterium, 

 Desmidium. 



Fig. 1097. 



Fi(t. 1096. A species of Diatomaceous Alga 

 (Biatoma marinum), dividiiii? into parts 

 by merismatic or flsoiparovs cell-division. 

 Tlie parts are been to be striated. 



Fig. 1097. Two Desmidiaceous Algse {Bocidium Ehrenbergii) after conjuga- 

 tion, with a renting or inactive spore between them. After Ralfs. 



Sub-order 5. VolvocinccB {fig. 1098). Henfrey diagnoses them 

 as follows: — "Microscopic bodies swimming in fresh water 

 by the aid of cilia arranged in pairs upon the surface of a com- 

 mon semi-gelatinous envelope, the pairs of cilia each belonging 

 to a green corpuscle resembling the zoospore of a confervoid, 

 imbedded in the periphery of the common envelope. Eepro- 

 duction by the development of each corpuscle into a new 

 colony, the whole being set free by the solution of the parent 

 envelope, or by conversion of the corpuscles into encysted 

 restiug-spores like those of Confervas." Examples : — Volvox, 

 Gonium. The members of this group are frequently regarded 

 as Infusorial Animalcules, but in all their essential characters 

 they closely resemble the Confervoidese. 



