Hydruracece 4."> 



chromatophores, which are of a yellow or pale brown colour. inn\ 

 be solitary and excentric, or sometimes two in a cell, and pyrenoids 

 are occasionally present. Vegetative multiplication occurs by 

 simple cell-fission and asexual reproduction takes place by me;m^ 

 of zoogonidia. 



The following seven families are the most important : 

 Fam. Hydruracea'. Hi/<lnirns Ag. 

 Fam. Cryptomonadinacece. Cryptomonas Ehrenb. 

 Fam. Ghrysomonadiiwcece. Xyttcrypta Ehrenb. Syntinr 



Ehrenb. Uroylena Ehrenb. 

 Fam. Dinobryacecs. Dinobryon Ehrenb. 

 Fam. Phwocapsacece. Plumcystis Lagerh. Pltceococcus 



Borzi. Phceosphcera West & G. S. West. 



Stichoyloea Chodat. Phceschizochlamys Lemm. 



PJueodactylon Bohlin. 



Fam. Choristocarpacece. Plenrocladia A. Br. 

 Fam. Phrvotliamniacece. Phceothamnion Lagerh. 



Only four of the above families are known to be represented 

 in Britain, but probably all the others will be found in more or less 

 abundance if searched for. Many of the plants of this order are 

 plankton-forms, and the families Cryptomonadinacese, Chryso- 

 moriadinaceff' and Dinobryacese are truly flagellate in character. 



Family 1. HYDRURACE^I. 



The plants are attached, branched, and consist of a colony of 

 unicells. The cells are at first spherical but afterwards become 

 almost spindle-shaped, and are embedded in large masses of 

 mucilage. They have one chromatophore and are destitute of a 

 cell-wall. Asexual reproduction takes place by zoogonidia which 

 are tetrahedric in form and possess one cilium 1 . They are only 

 produced in the branches, two or four from each cell, and they 

 germinate directly. After having come to rest, the zoogonidia 

 attach themselves by the clear apex (at which point the cilium 

 was inserted) and secrete a stalk-like mass of mucilage. This cell 

 is the beginning of a new colony which is developed subsequently 

 by its repeated divisions. Certain of the peripheral cells take on 

 apical growth and produce branches. Resting spores (akinetes) 

 have also been observed by Lagerheim. 



1 Cfr Lagerheim in Ber. Deutsch. Bot. Gesell. 1888, p. 80, tig. xylogr. 13. 



