344 



BOTANY 



In many Peridineae of the plankton the plates bear special wing-like expansions 

 (Fig. 269 A) or the cells have long horn-like processes. These adaptations enable 

 the organisms to remain floating in the water ( 12 ). 



In some Peridineae the chromatophores are only represented l>y colourless 

 leucoplasts. Such species live either as saprophytes or in the same way as 

 animals. iliiniiiiMliii! inn hyaliiiuin is a colourless, naked, fresh-water Conn, the 

 protoplast of which for the purpose of absorbing nourishment loses its cilia 

 and assumes the form of an amceba ; in this condition it encloses and digests 

 small Algae ( 1:| ). 



Reproduction is by cell-division and also by means of swarm-spores. In the 

 latter case the protoplast escapes from the membrane and either shortly Conns a 

 new wall or divides into several swarm-cells (Fig. 268 C}. Thick-walled resting 

 cells (cysts) also occur. ZEDERBAUKK has recently observed a process of sexual 

 reproduction (the conjugation of protoplasts escaping from two similar cells to 

 form a zygote) in Ceratium ( 14 ). 



CLASS VI 



Conjugatae (" ls ) 



\J 



u 



This class of green freshwater Algae includes unicellular and 

 simply filamentous forms, and is clearly distinct from that of the 



Chlorophyceae. The Conjugatae 

 are most nearly related to the 

 Diatomeae, with which they might 

 be united in the group of the 



fZygophyceae, since the two classes 



^B^fc- J&Sb. /^dJEB-hT^. sn w essential agreement in their 

 ir^r* :{fffP f yj^p } mode of sexual reproduction. This 

 consists in the conjugation of two 

 equivalent gametes to form a xygote 

 , or zygospore. Asexual reproduction 



ating cells each divided into two daughter by means of SWarm-SpOl'eS is Wai iting 



cells ; 2, S, stages of conjugation ; , mature j n Jj ot h claSSeS.aild Since the (SimeteS 



zraotes. (After ABCHXR : from OLTMANN'S , . , -, .,, .,. ., 



jigae.) also are unprovided with cilia these 



forms are also classed as Acontae. 



The cells of the Conjugatae which increase in number by cell-division 

 are uninuclear, and differ from those of the Diatoms in having a cell- 

 wall which is not silicified and in the presence of large green chloro- 

 plasts of complicated structure. 



1. The Mesotaeniaceae, the simplest of the unicellular Conjugatae, include only 

 a few genera. They are distinguished from the following order by the cell-wall of 

 the shortly cylindrical cells not being formed of two halves. The mode of eon 

 jugation presents some differences. In :>',///<. /^/w (Fig. 270) the protoplasts of 

 the conjugating cells first divide and the daughter cells unite in pairs to form the 



