Autosporacede 



197 



Sub-family OocYSTE^;. This sub-family is characterized by the globose 

 or ellipsoid cells (curved or even sublimate in Nephrocytium) which are 

 frequently retained within the distended wall of the old mother-cell. In 

 nearly all cases the cells possess strong cellulose walls, which in the genus 

 Scotiella (Fritsch, '12 A) of the polar and alpine snow-flora, are furnished 

 with wing-like ridges extending from pole to pole (consult fig. 122 G L}. 

 In Oocystis the cell-wall generally exhibits a slight thickening at each pole. 

 Each cell contains from one (N ephrocytium, Scotiella) to many (Eremosph&ra, 

 Excentrosphterct) chloroplasts, parietally disposed except in Oocystis natans 

 (Lemm.) Wille, and with or without a pyrenoid. In Eremosphtera the cell is 

 exactly spherical, and the parietal chloroplasts are small and very numerous. 

 The cells of this genus are much the largest of the unicellular Protococcales, 

 attaining a diameter of 200 JJL, and the centrally-placed nucleus is cor- 

 respondingly big (fig. 123 A). The genus Glwotfenium, which has recently 



Fig. 123. A, optical section of Eremoxph&ra viridis De Bary, to show parietal disposition of 

 numerous chloroplasts and centrally-placed nucleus, x 300. B and C, ExcentrospJisera 

 viridis Moore. B, surface view showing closely packed parietal chromatophores ; C, escape 

 of gonidia, x about 190 (after Moore). 



been re-investigated by Transeau ('13), is remarkable for the presence of 

 a black pigment in the old walls of the mother-cells so arranged as to form 

 bands and caps (fig. 115 ^4). 



Reproduction takes place by the division of the mother-cell into 2, 4 

 or 8 autospores, which grow and usually attain their full size while within 

 the greatly distended wall of the mother-cell (figs. 121 E and G; 122 B). 

 In Oocystis and Nephrocytium several generations may be contained within 

 the remnants of an old mother-cell-wall. In Nephrocytium ecdysicepanum 

 W. & G. S. West ('96) and in Oocystis glceocystiformis Borge ('06) several 

 generations are aggregated in a fan-shaped manner owing to the ecdysis 

 but incomplete dissolution of the old mother-cell-walls. Sometimes the wall 

 of the mother-cell becomes converted into a structureless mass of jelly in 

 which the daughter-cells are embedded (fig. 121 D). In Ecdysichlamys the 



