HOW TO KNOW THE FRESH-WATER ALGAE 



215a Thallus a tube-like strand (sometimes forked), containing many 

 lamellations (layers); cells at the tips of the tubes. Fig. 154... 



HORMOTILA 





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Fig. 154. 

 Borzi. 



Hormotila m ucigena 



Figure 154 



This curious plant is a branched 

 colonial form by virtue of the fact 

 that as the cells divide they se- 

 crete mucilage and construct gelatinous strands that branch and re- 

 branch, the cells always occurring at the distal ends of the strands. 

 The plant (one species only being known) is classed near Gloeocystis 

 (Fig. 41) in the Tetrasporales (Palmellaceae). 



215b Thallus not as above 216 



216a Cells located at the ends of undivided tubes, the cell bearing a 

 seta with a sheathed base. See Fig. 62. . .CHAETOSPHAERIDIUM 



216b Cells without setae 217 



217a Cells constricted in the middle, occurring at the ends of tubes 

 which are united in colonies that are impregnated with lime. Fig. 

 155 OOCARD1UM 



Fig. 155. Oocardium stratum Naeg. 



This is a very rare desmid, or at least it 

 has been reported but few times, probably 

 because it is overlooked by collectors. The 

 Cosmarium-like cells occur in colonies at 

 the ends of branched gelatinous strands and 

 are inclosed in a firm sheath of lime. They 

 are to be sought on encrustations of rocks in 

 dripping or flowing water. 



Figure 155 



217b Cells not constricted in the midregion, not arranged as above. .218 



99 



