Guilliermond - Atkinson 



42 



Cytoplasm 



encountered in many zoospores of the Chlorophyceae. In the 

 Diatomaceae, a group often considered as closely related to the 

 flagellated algae, there are a small number of large, plate-like 

 chloroplasts, often only two, occupying a marginal region of the 

 cell. 



In the Chlorophyceae, the chloroplasts appear as large organ- 

 elles of rather complex structure. In the Ulothricales, for ex- 

 ample, there is only one chloroplast per cell (Ulothrix, Draparnal- 

 dia) in the shape of a deeply dentate ring girdling the elongated 

 cask-shaped cell near its middle. In the Siphonales and the Siphono- 

 cladiales, the chloroplasts are variously disposed and appear in 

 many different shapes. There may be one single chloroplast per 

 chamber or cell, distributed throughout the cytoplasm in the shape 

 of a network whose numerous swellings are occupied by pyren- 

 oids (Cladophora) , whereas in algae, such as Acetabularia, 







.chr. 



L — ) 



1 



A. rhr^ 



Fig. 12. — Chloroplasts of the Chlorophyceae. 1, Draparnaldia 

 (After ScHMiTZ). 2, Zygnema. 3, Mougeotia scalaris. Two views. 

 (After Palla). 4, Oedogonium. (After Schmitz). chr, chloroplast. 

 py, pyrenoid. n, k, nucleus, a, s, starch, ky, tannin bodies of Palla. 



the sections enclose numerous chloroplasts of irregular con- 

 tours, each chloroplast carrying several grains of carotin but not 

 having any pyrenoids and starch grains (Mangenot and Nardi). 

 In Vaucheria, the chloroplasts, distributed in great numbers in the 

 tubular thallus and never enclosing starch, are bodies of the dimen- 

 sion and form of those found in the phanerogams. They are also 

 small in Caulerpa and Derbesia, which, although lacking in pyren- 

 oids, seem often to elaborate starch by a rather strange and still 

 imperfectly known process (Ernst, Czurda). 



In the Conjugatae, the chloroplasts are of a very complex form 

 to which particular attention must be called. There are only a 

 few or even only a single one present in each cell. Thus in Cos- 

 marium and Zygnema there are found in each cell two large star- 

 shaped chloroplasts whose long delicate arms radiate from a py- 

 renoid situated in the center. In others, Mougeotia for example, 

 the single chloroplast is a large smooth plate. A chloroplast of 

 M. laetevirens may attain a length of SOOix and a width of more 



