846 RECORD OF CURRENT RESEARCHES RELATING TO 



reversed every few seconds, a moment of rest or of confused move- 

 ment of the particles among one another preceding the reversal of the 

 direction. 



The cause of this peculiar ebb and flow has not, he believes, been 

 previously recorded. 



The clear spaces at the ends of the fronds of the Closterium are 

 really contractile vesicles, and careful observation under the above 

 powers shows that they are undergoing incessant though slight change 

 of form. The contraction of any part of the surface of the vesicle is 

 followed by an immediate rush of the surrounding fluid to fill the 

 vacuum thus formed, and the direction of the currents, where the 

 transparent spaces allow them to be observed, may be clearly con- 

 nected with the corresponding contraction of one or other part of the 

 vesicle. In stating their flow to be in lines or bands, it is merely 

 intended to describe the general appearance of the action. The whole 

 space between the endochrome and the cell-wall is, doubtless, filled 

 with the fluid ; but the transverse section of the former would pro- 

 bably present a fluted or corrugated form, corresponding to its longi- 

 tudinal disposition in belts of denser matter ; and the flow of the 

 surrounding fluid may probably be determined by the channels formed 

 by this fluted structure. 



These movements may be found to have their parallel in the 

 smaller species of Closterium, and in other genera of Desmidieaa in 

 which there is a terminal vesicle. 



It is to be noted that the flow of cell-contents, while it is 

 actuated by the contractile motions of the vesicle, is a phenomenon 

 wholly distinct from the swarming of the larger particles within it, 

 the functions of which are, Mr. Wills fears, still hidden in entire 

 obscurity. 



Endochrome of Diatomacese.* — A writer in the ' English 

 Mechanic,' referring to M. Petit's paper, of which we gave a trans- 

 lation at p. 680, says, " The English student of the chromatology of 

 plants will not fail to be surprised, on reading M. Petit's article, to 

 find no reference to the valuable work done by Mr. Sorby in this 

 department of scientific research, and we can only come to the con- 

 clusion that M. Petit is, as so many of his countrymen appear to be, 

 extremely ignorant of the present position of vegetable and animal 

 chromatology in England. This is very much to be regretted, as 

 there is no doubt that had M. Petit been familiar with the valuable 

 paper read by Mr. Sorby before the Eoyal Society in 1873, and 

 published in the ' Proceedings ' of the Eoyal Society in that year,-j- 

 his conclusions would have been much modified, and the ground 

 covered in his research not only greatly extended, but more minutely 

 examined. There is no doubt, for instance, that M, Petit would 

 have foimd reason to believe that his phycoxanthine is identical with 

 that of Kraus, and, as Mr. Sorby has shown, is really a ' mixture of 

 two or three distinct colouring matters, which can easily be separated 

 and do occur separately in other plants.' The true phycoxanthine 



* ' Engl. Mech.,' xxxi. (1880) p. 573. t No. 146, vol. xxi. 



