Simplest Forms of Life. 233 



Spirogyra. Spores spherical ; on drying, the filaments 



become brown. 

 *Z. cruciatum, Ag. Cells 0.04-0.044 d.; l.=:i-2 d. Common in 



standing water as floating, yellowish-green masses. 



[Spore-coat minutely punctate.] 

 Z. stellimum, Ag. Cells 0.024-0.033 d. ; l. = i-3 d. Common. 



[*Z. insigne, Ktz. Deep green or yellowish-green, conjugation scala- 

 riform, sometimes lateral, spore-coat smooth.] 



4. Gen. Zygogoniutn, Ktz. Cells with two irregular chlorophyll 



plates, enclosing starch grains. Copulation as in Zygnema, 

 but the spore forms in the connecting tube. The species 

 live mostly out of water on moist ground. All have a 

 purple-violet coloring matter which predominates in many 

 during life, but always when dried. 

 Z. Agardhii, Rh. (Z. ericetorum, Ktz.). Common almost every- 

 where. 



5. Gen. Pleii7-ocarpus, A. Br. {Mougeotia, Ag.). Chlorophyll 



in fine grains, equally distributed, often contracted to a 

 longitudinal band. Copulation geniculate, often unfruit- 

 ful, or lateral as in Rhynchonema, but with spores formed 

 in the connecting tube. 

 ^P. mirabilis, h.'Qr. {Moi^geotia genuflexa, h.^.). Cells 0.03-0,036 

 d.; l. = 2-4 d. Forms light-green masses in standing water. 



6. Gen. Sirogo?iium, Ktz. Chlorophyll in longitudinal, pearly 



strings. Copulation geniculate without connecting tube. 



Spore in one of the two cells. 

 S. sticticum, Ktz. Cells 0.037-0.05 d. ; l. = 4-5 d. Two to four 



slightly bent bands. Dirty-green, intricate masses in 



standing water. 

 [*5". retroversiim. Wood. Chlorophyll band i, in spiral 1-9 turns, 

 fertile cells very tumid, retroverted.J 



7. Gen. Mesocarpus, Hass. Cells similar to Pleurocarpus. 



Copulation geniculate (often growing ladder-shaped later). 



Spore in turgid, connecting tube. Filaments generally 



live single among other Algae in standing water. 

 *M. scalaris, Hass. Cells 0.016-0.002 d. ; l. = 2-8 d. 

 *M. parvulus, Hass. Cells 0.007-0.009 d.; 1. = 1.5^-12 d. [Spores 



fuscous.] 



8. Gen. Staurospermum, Hass. Chlorophyll evenly distributed, 



often contracted into a longitudinal band. Copulation 



