312 Ulotrichales 



cartilaginous stratum, and are unicellular or rarely bicellular. In the 

 formation of the hairs the outer layers of the thick cell-wall are broken 

 through by the innermost layer, and on the completion of development the 

 hair is cut off from the supporting-cell by a basal wall (fig. 204 B). 



Each cell possesses a reticulated parietal chloroplast with many pyrenoids 

 (fig. 204 C). There are also many oil-drops of variable size, which are green 

 in the inner parts of the thallus, but are of a golden-yellow or orange colour 

 in the outer cells exposed to light. 



Keproduction takes place by akinetes and aplanospores. The akinetes 

 are formed only from the terminal cells of the branches, which swell out 

 (up to 60 //. diameter), become rounded, and develop thick walls (fig. 204 E). 

 They are finally set free by the dissolution of some of the middle lamellae of 

 the separating- wall. The aplanosporangia are also formed from the terminal 

 cells of those branches which do not bear hairs. The aplanospores (5 10 //, 

 in diameter) arise in large numbers by free-cell-formation and though at 

 first angular, soon become rounded and furnished with a strong cell-wall 

 (fig. 204 D). They are eventually set free by the dissolution of the mother- 

 cell-wall. 



Zoogonidia and gametes are unknown. 



In the multinucleate character of its ' cells ' and in the nature of the 

 chloroplast Wittrockiella would appear to be related to the Cladophoracese ; 

 on the other hand, the branching of the filaments, the accumulation of 

 much oil, and the formation of akinetes suggests a relationship with the 

 Trentepohliacese. The development of hairs is a character in common with 

 the Chaetophoraceae. Wille considers that the family is correctly placed in 

 the Ulotrichales, but there are almost equally good reasons for placing it 

 in the Siphonocladiales. 



Wittrockiella paradoxa Wille ('09) was originally discovered in brackish-water ditches 

 in southern Norway. It has since been found by G. T. Moore on the coast of Massachusetts 

 (vide Collins, '12). 



Family Aphanochaetaceae. 



This is a small family which includes only the one genus Aphanochsete 

 A. Braun, 1851 (= Herposteiron Nageli, 1849) 1 , which is an epiphyte on 

 larger Algae and often on aquatic phanerogams. The thallus is creeping 

 in habit and consists of short irregular filaments, with a few slightly 

 attenuated branches. Most of the cells of the thallus possess one or several 

 bristle-like setae or hairs, cut off from the cell which bears them by a basal 

 septum. The bristles are merely greatly elongated cells, slightly swollen at 



1 Klebahn ('93), Huber ('94) and Nordstedt (in Botaniska Notiser, 1906, p. 118) have given 

 cogent reasons for the retention of the generic name Aphanochsete. 



