H ■mmr 



G 55Zt 



Fig. 62. Mougeotia. A-E, M. mirabilis, stages in conjugation 

 through loss of cell wall. F, normal conjugation in M. mirabilis. 

 n =new walls cutting off zygote. G-I, stages in lateral conjugation 

 of M. oedogonioides. J, two azygotes in M. mirabilis. (A-F, after 

 Czurda; G-I, after Fritsch; J, after Kniep.) 



Mesotaeniaceae : Mesotaenium (meso, middle; taenium, band). 

 Fig. 63 



This is an example of one of the saccoderm desmids, which as a 

 group are characterized by a smooth wall in one complete piece 

 and without any pores. The rod-shaped cells of Mesotaenium are 

 single, have no median constriction, and are circular in transverse 

 section. The chloroplast in this particular genus is a flat axile plate 

 containing several pyrenoids, whilst in some species the presence of 

 phycoporphyrin imparts a violet colour. The inner cell wall is 

 composed of cellulose and the outer of pectose. Multiplication 

 takes place by cell division, the daughter cells being liberated by 

 dissolution of the middle lamella after a constriction has been 

 formed, though in some cases this may not occur until a number of 

 cells have been enclosed in a common mucilaginous envelope. 

 Sexual reproduction is by means of conjugation, two processes 

 being put out just as in the filamentous forms : these unite and then 



III 



