648 SCIENCE PROGRESS 



the Endosphcera-co\ony . In both Endosphcera and the Hydro- 

 dictyaceae the fusion of the gametes leads to the production of 

 a resting-cell, which sooner or later gives rise to a new colony. 

 It seems probable, therefore, that the Hydrodictyaceae are a side- 

 line of evolution from the stock of the Protococcales, and that 

 this line possibly branched off from the Protococcaceous series. 

 The relationship to the Scenedesmaceae is, however, also very 

 close, for there is obviously not very much difference between 

 the mode of formation of the daughter-colonies in a Ccelastrum 

 (for instance) and that in the Hydrodictyaceae. The polyhedron- 

 stage of the latter, moreover, bears an astonishing resemblance 

 to the genus Tetraedron, 1 which is a member of the Scenedes- 

 maceae. Lastly, we may note that in the multinucleate cells of 

 their colonies the Hydrodictyaceae again approach the Proto- 

 coccaceae, while it has been shown that in the very young cells 

 of Hydrodictyon the chloroplast is a simple plate (Artari i), quite 

 easy to bring into line with that of a Chlorococcum, etc., although 

 in the mature condition it is a complicated reticulated structure 

 with numerous pyrenoids. 



We have now completed our survey of the numerous uni- 

 cellular and colonial forms found among the lower green 

 Algae, and subsequently will turn our attention to the higher 

 filamentous types. 



1 In this connection it is of some interest also that Wille (70) has recently 

 shown that the genus Oocystis (Scenedesmaceas) forms similar polyhedra as 

 resting-stages. 



( To be continued) 



