CRYPTOGAMS 



.315 



Class IV 



Peridineae 



The Peridineae or Dinoflagellata, were formerly classed with the lowest animals, 

 but are, in reality, unicellular Thallophytes. They live for the most part in salt 

 water, and form, together with the Diatomeae, an important part of the plankton 

 floating on the surface of the ocean. Their cell plasma contains a nucleus, a com- 

 plicated system of vacuoles, and light yellow, tabular chromatophores. The pres- 

 ence of these chromatophores in the Peridineae has, in particular, been considered 

 indicative of their vegetable nature. The Peridineae 

 are further characterised by two long protoplasmic 

 cilia or flagella, to the vibrations of which the move- 

 ments of the cells are due. The flagella spring from 

 the ventral side of the cells, and lie in two furrows, 

 which cross each other at right angles, on their 

 surface (Fig. 234). Only a few Peridineae are entirely 

 naked ; most of them have peculiarly sculptured cell 

 walls, consisting of intersecting cellulose plates or 

 ribs. They multiply by division, and in the autumn 

 form thick -walled cysts, in which condition they 

 pass the winter. Conjugation has not been observed. 



In addition to the forms which, like Algae, sus- 

 tain themselves by means of assimilating yellow 

 chromatophores, there occur also colourless Peri- 

 dineae, whose chromatophores are only represented 

 by colourless leucoplasts. Such species, although 

 nearly related to the brown Peridineae, live either as saprophytes or in the same 

 way as animals. Gymnodinium hyaMnum, a, colourless, naked, fresh-water form, 

 exhibits a mode of life resembling that of a Myxomycete. For the purpose of 

 absorbing nourishment it loses its cilia and assumes the form of an amceb'a ; in 

 this condition it encloses and digests small Algae. 



Fig. 234. — Peridinium bipes, ven- 

 tral view. (After Schilling, 

 x 750.) 



Class V 



Conjugatae 



In the class of the C'onjugatae is included a large independent 

 group of green, fresh-water Algae, comprising over 1000 species, in 

 the form either of solitary cells or filamentous rows of cells. They 

 derive their name from their peculiar mode of sexual reproduction, 

 which consists in the conjugation of two apparently similar cells, 

 resulting in the formation of a zygospore. They are in this respect 

 sharply distinguished from all the other green Algae, the Chlorophyceae, 

 from which they may be distinguished also by the absence of any 

 asexual mode of spore-formation, and by the complicated structure of 

 their green chromatophores. 



