100 Chlo i 'ophycece 



A C). These two species are widely distributed all over the British Islands, 

 and they have a decided preference for the neighbourhood of towns, being 

 found frequently under walls and as a green carpet between the paving-stones 

 of quiet streets. They require little moisture and can withstand considerable 

 desiccation. Associated with them are generally numerous Rotifera mdgaris 

 and testaceous Rhizopods such as Trinema acinus. Prasiola furfiiracea 

 Menegh. is probably a form of P. crispa. 



Order V. MICROSPORALES. 



This order was first established by Bohlin to include those 

 curious plants which belong to the genus Microspora. It seems 

 at first sight to be giving undue prominence to a small group of 

 aberrant Algas, but at the same time it removes a difficulty, as 

 these plants cannot well be placed in any of the other orders of 

 green Algas. 



The thallus is filamentous and unbranched, and the cell-walls 

 frequently become broken up into H -shaped pieces. The cells are 

 uninucleate, with a large reticulated chloroplast occupying almost 

 the entire inner surface of the cell- wall, and destitute of pyrenoids. 

 The affinities of the order are very doubtful. 



Family 1. MICROSPORACE^. 



This small family includes only one genus. The thallus is 

 filamentous and simple, and the cells are cylindrical. The cell- 

 walls are composed of cellulose, are either homogeneous or more or 

 less distinctly lamellose, and of a similar structure to those of 

 Tribonema (Conferva), the cells often becoming disarticulated into 

 H -shaped pieces. A single nucleus of considerable size is present 

 in the centre of each cell. The chloroplast is disposed on the walls 

 of the cell and may be band-like or sheet-like, covering more or less 

 the entire cell-wall. It is usually areolated or reticulated, and 

 really consists of a fusion of numerous cushion-like, chlorophyl- 

 laceous masses to form a stout areolated structure. There are no 

 pyrenoids, but scattered granules of starch are often present. 



Asexual reproduction takes place by the formation of aplano- 

 spores which become hypnospores (fig. 37 C and F) ; also by the 

 production of biciliated or quadriciliated zoogonidia, one or two 

 of which are found in a cell. Sometimes several small micro- 

 zoogonidia are produced in a cell. The zoogonidia germinate 

 directly. 



