288 



Ulotrichales 



It is necessary to make some special mention of the genus Schizomeris Kiitzing (1843). 

 Hazen ('02) states that he has no doubt concerning the validity of the genus Schizomeris, 

 but that its affinity seems to be with the Ulvaceee rather more than the UlotrichaceEe. 

 The filaments are attached to rocks and stones in streams ; they are attenuated at both 

 base and apex, and longitudinal division of the cells occurs. The manner of the dispersal 

 of the zoogonidia is very striking and unlike anything in the Ulotrichacese. Hazen 

 remarks that 'all the dissepiments in the upper part of the thallus appeared to be 

 softened or broken down, and the masses of zoospores escaped through the open funnel 

 formed by the outer cell- wall.' 



Family Microsporaceae. 



This family includes only the one genus Microspora (Thuret, 1850; 



em. Lagerheim, 1888) 1 the species of 

 which are amongst the most abundant 

 and widely distributed of freshwater 

 Algae. The filaments are cylindrical 

 and unbranched, and from the very 

 earliest stages of development are 

 free-floating. The cell-wall varies in 

 character in the different species of 

 the genus. In some it is apparently 

 homogeneous, but in others it is 

 distinctly lamellate, attaining its 

 greatest thickness and irregularity in 

 Microspora amcena var. irregularis 

 W. & G. S. West ('06). The lamellae 

 consist of cellulose. The statement 

 so frequently made that the lamellae 

 of the wall are so laid down that the 

 filaments become disarticulated into 

 H -pieces is only true of certain 

 species of the genus. This occurs 

 in M. tumidula, in the typical forms 

 of M. amcena and M. Lofgrenii, and 

 to some extent in M. floccosa and 

 M. quadrata. In the two last- 



Fig. 184. A, Microspora amcena (Kiitz.) Lagerh. 

 B aud C, ? M. abbreviata (Rabenh.) Lagerh.; 

 B, vegetative filament ; C, filament with 

 aplanospores (a). D, M. pachyderma (Wille) 

 Lagerh. E, single vegetative cell of M. amcena 

 var. crassior Hansg., showing the reticulated 

 cliloroplast. The indistinct blur in the centre 

 of the cell indicates the position of the nucleus. 

 F, fragment of filament of M. amcena with 

 aplanospore (a). All x 520. 



mentioned species the disarticula- 

 tion is only partial and often irregular, parts of the lateral walls usually 



1 The main conclusions of the paper on "The Structure, Life-History and Systematic 

 Position of the genus Microspora," which was communicated by the present author to the 

 British Association at the Birmingham Meeting in September, 1913, are embodied in this 

 account of the Microsporacese. 



The recent paper by Meyer on Microspora amcena (December, 1913) adds nothing of importance 

 to the present account. Meyer's figure of the formation of ' akinetes ' (fig. 15) represents the 

 formation of aplanospores. 



