Microsporacex 



289 



becoming mucilaginous. In the common species M. stagnorum 1 the fila- 

 ments almost always break at or near the transverse walls. 



The cells are uninucleate, the nucleus in many cases occurring in a 

 fairly broad band of cytoplasm stretching across the median part of the cell. 



There is but one chloroplast in each cell, and the nature of this 

 chloroplast is the chief distinguishing feature of Microspora. It consists 

 of a number of small parietal green cushions which are united in a most 

 irregular way to form a reticulum. The very irregularity of this reti- 

 culum, the form of which may be quite different even in adjacent cells 





Fig. 185. A, ? Microspora abbreviata (Rabenh.) Lagerh., three cells to show the chloroplast, 

 x 1000. B, two cells of M. tumidula Hazen, showing form of chloroplast, x 1000. C and 

 D, portions of two filaments of M. stagnorum (Kiitz.) Lagerh. snowing characteristic 

 variations in the chloroplast, x 500. E, escape of zoogonidia in M. tumidula Hazen, in 

 which the cell-walls break up into H -pieces, x 500. F, escape of zoogonidia in M. floccosa 

 (Vauch.) Thur., in which the H -pieces are more irregular and there is slight gelatinization 

 of the wall, x 500. G, escape of zoogonidia of M. stagnorum, in which H -pieces are never 

 formed but the wall is completely converted into mucilage, x 500. H J, germination of 

 zoogonidium of M. stagnorum, x 500. 



(consult fig. 185 D), is one of the leading characters of the genus. The 

 cushions of the chloroplast are usually spread over both lateral and terminal 

 walls, and in some instances (frequently in M. stagnorum and occasionally in 

 M. floccosa) they are disposed as irregular constricted bands united to form 

 a loose network (fig. 185 (7). There are no pyrenoids, but starch is stored in 

 the form of small granules. 



1 The figure given by Hazen ('02, t. 24, f. 12) of the disarticulation of a filament of M. stag- 

 norum during the liberation of zoogonidia does not agree with any state of this alga observed by 

 the present author. 



W. A. 19 



