170 



FRESH-WATER BIOLOGY 



241 (240) 



Individual cells flask-shaped, each with a long slender hair from 

 the smaller portion Chaetosphaeridium Klebahn. 



Chromatophore 

 parietal, with one 

 pyrenoid. Repro- 

 duction by zoo- 

 spores, four of 

 which are produced 

 in a cell. Horizon- 

 tal divisions of the 

 cells also occurs, 

 the lower of the 

 daughter cells pass- 

 ing gradually to the 

 side of the upper 

 one. 



Chaetosphaeridium 

 is widely distrib- 

 uted in the United 

 States though 

 rarely occurring in 

 quantities exceed- 

 ing a few cells at a 

 time. 



These are usu- 

 ._ ally attached to fil- 

 amentous algae and 

 are inconspicuous, 

 though the long 

 setae are usually 

 somewhat promi- 

 nent 



FIG. 236. Chaetosphaeridium pringskeimii Klebahn. X about 425. (After Hazen.) 



242 (234) The zoosporangia different from the vegetative cells. 



1 Subfamily CHROOLEPIDEAE . . 243 



243 (244, 245) Plant minute, tree-like in its branching; reproduction by 



zoospores Microthamnion Nageli. 



Branches from the upper end of a cell and not sepa- 

 rated by a membrane; obtuse at the tip; color pale; 

 chromatophore a parietal band with no pyrenoid. Zoo- 

 spores formed in zoosporangia at the ends of filaments. 



FIG. 237. Microthamnion kiitzingianum Nageli. 

 (Original.) 



X6oo. 



244 (243, 245) Plant coarse, irregularly branched, partly erect and partly 

 creeping on stones and trees; when aerial, often colored red 

 by haematochrome. Membrane thick; reproduction by 

 zoospores and gametes Trentepohlia Martius. 



Chromatophores many, irregular discs, without pyre- 

 noids; gametangia and zoosporangia mostly terminal; 

 gametes and zoospores similar, being egg-shaped, with 

 two cilia and haematochrome, but no definite pigment 

 spot. A palmella condition may occur. 



These are sometimes referred to as the aerial algae 

 because they exist principally in the air and form often 

 bright -colored incrustations on the bark of trees and 

 stones. They are not infrequently found in connection 

 with lichen fungi. 



As the Trentepohlias are principally aerial, the lib- 

 eration of the zoospores and gametes can occur only at 

 the time of a rain or in the presence of a heavy dew. 



FlG. 238. Trentepohlia wainoi Hariot. X 125. (After 

 Collins and Hariot.) 



