148 THE BOTANICAL MAGAZINE. LVoi. xxxn. No. 379. 



axis lies always in the cross-wise position to the axis of the 

 chain when the latter is seen from the broader surface. The 

 "plasma" membrane inherited from the mother-frustule be- 

 comes more or less rigid, thin coating, and is now called 

 perizonium. Thus the auxospore is completed. 



A new menbrane is formed inside the perizonium, holding 

 the whole content in it. The content contracts itself with the 

 new menbrane, coming off from the perizonium in a manner 

 of plasmolysis. (Fig. 4.). One side of the contracted mass 

 assumes a definite shape to form the upper surface of the 

 epitheca ; at the two corners of the surface the beginnings of 

 the setae become soon visible which pierce out through the 

 perizonium ; then the lateral surface is limited ; and finally, 

 the hypotheca. A new frustule with recovered size is thus 

 formed. The breadth of the new frustule is about 3 times as 

 large as the mother-frustule. (Fig. 5.). From the beginning 

 of the spore-formation till the new frustule was completed it 

 took, in our cases, seven hours in average. 



As soon as the enlarged new frustule is completed, it 

 prepares for the cell-division. The nucleus and the chromoplast 

 are divided into two, height of the frustule is increased, and 

 the setae are given forth at the points in the midway of the 

 first-formed, two lateral setae. (Fig. 6.). 



The perizonium can not extend itself to follow the size- 

 increase of the new frustule. It ruptures in one side and only 

 a part of the first-formed epitheca remains stuck within it. 

 The ruptured margin is hardly visible owing to its extreme 

 thinness. When the frustule has multiplied successively as to 

 count 7—9 in number, the chain breaks away from the 

 remnant of the perizonium. (Fig. 7.). 



The primary valves of the terminal frustules of the chain 

 are markedly convex in the middle. (Fig. 8.). In ordinary 

 chains this sort of individual peculiarity is not to be noticed. 

 Schutt 15 also illustrates a similar form in the daughter-chain 

 of Ch. contortum Schutt. 



The axis of the daughter-chain is always perpendicular to 

 that of the mother-chain. When the latter is observed from its 



