Simplest Forms of Life. 231 



chlorophyll in two star-like groups. Zygnema, Ktz. 



Spore in the connecting tube. Zygogonium, Kt. 



lateral and knee-shaped, on the same fila- 

 ment. Spore in the connecting tube. Pleiirocarpus, A. Br. 

 geniculate, never lateral. 



Spore in one of the copulating cells. Sirogoniiim, Ktz. 



Spore in connecting tube, 



which is turgid, Mesocarpus, Hass. 



which is constricted, 



spore cruciform, Staurospcriiiiim, Ktz. 



spore spherical, Craterospertnittn, A. Br. 



I. Gen. R/iynchone»ia, Ktz. Chlorophyll in i or 2 spiral 

 bands. Copulation between two cells of the same fila- 

 ment, not direct, but through external continuations grow- 

 ing out and meeting, through which, after absorption of 

 the separating walls, the entire contents of one cell passes 

 over into the other, and there unites with its plasma to 

 form a single spore. Numerous species. 

 R.vesicata, Ktz. Cells 0.018 — 0.022 d.; 1.3=3-4 d. Cell-ends 

 forced inward. One chlorophyll band with iJ^-2 turns. 

 Spore egg-shaped, in turgid cell. 

 R. Hassallii, Ktz. Cells 0.028 — 0.035 d.; l. = 3^ — 7 d. Two 

 bands. 

 [Owing to the fact that some species copulate in two ways, partaking 

 of the characters of both Spirogyra and R/iync/ioneina, as here distin- 

 guished, some authors have discarded the latter genus and place the 

 species under Spirogyra. The two following are examples, found in 

 this country : 



*Sp. (J?.) clo7igata, Wood. Sterile joints, much longer than broad ; 

 fertile joints, much shorter, greatly swollen ; cell-wall at each end, pro- 

 duced or folded in, one chlorophyll filament, spiral lax, generally 7 

 turns. 



*Sp. (7?.) pidchella. Wood. Sterile joints 2-3 times longer than 

 broad, fertile joints somewhat swollen, single chlorophyll band 3-4 

 turns ; cell-wall at each end produced or folded in.] 



2. Gen. Spirogyra, Link. In appearance very similar to the 

 preceding, only to be distinguished while fruiting. In 

 this condition ladder-like from the copulation of two op- 

 posite cells of neighboring filaments which extend con- 

 tinuations toward each other. By the disappearance of 

 the separating wall, when these come in contact, a cylin- 

 drical combining tube is formed between the two cells, 



