224 



ELEMENTS OF" BOTANY. 



conjugation by leaving the Spirogyra filaments in very cold water over 

 night, and in this way the successive steps of the conjugating process 

 may be studied by daylight. In such ways the series of phenomena 

 shown in Fig. 195 has been clearly made out. If the student cannot 



follow these operations under the mi- 

 croscope, he may at least by looking 

 over the yellower portions of a mass of 

 Spirogyra find threads containing fully 

 formed zygospores, like those shown 

 in B, Fig. 195. 



A'LGM. 



Fig. 195. — Formation of Spores 

 by Conjugation in Spirogyra. 

 A, two filaments of Spirogyra side by 

 side, with tbe contents of adjacent 

 cells uniting to form spores z. At 

 the bottom of the figure the pro- 

 cess is shown as beginning, at the 

 top as completed, and the cells of 

 one filament emptied ; B, a single 

 filament of another kind of Spiro- 

 gyra, containing two spores, one 

 lettered?;. (^ magnified 240 diame- 

 ters, J3 150 diameters.) 



274. Characteristics of Algce. 

 — The Protococcus and the Spi- 

 rogyra are two common fresh- 

 vsrater examples of the kind of 

 plants classed under the general 

 name of AlgcB, a group of which 

 the largest and most interesting 

 examples are to be found among 

 the seaweeds. Algae are all 

 aquatic, or at least live usually 

 in damp places ; they contain 

 chlorophyll, and are therefore 

 capable of absorbing carbonic 

 acid gas and fixing carbon ; few 

 algse are parasitic or saprophytic. 

 In fact, the main distinction be- 

 tween this group and the fungi 

 lies in the self-supporting char- 

 acter of the former plants and 



the parasitic or saprophytic 

 (§ 151) character of the latter. For this reason the two 

 groups, based on the characteristic behavior or mode of life of 

 their members, rather than on the real relationships of the 



