246 SUMMARY OF CURRENT RESEARCHES RELATING TO 



comparison with the near relations of the fungal parts of the lichens 

 with the other ascomycetous fungi." 



Cooke's British Fresh-water Algae. — The existing books on British 

 fresh-water Algae are so much out of date that a new one will be very 

 welcome to algologists and microscopists. The first part of Dr. M. 

 C. Cooke's work is now published, and contains the Palmellaceae with 

 11 coloured plates and 32 pages of text, and is intended to be 

 followed by part 2, the Protococcacefe and Volvocinese, and part 3, 

 the Zygnemaceae. The Desmidieae and Diatomaceae are not intended 

 to be included. 



Diatoms in thin Rock Sections.— At p. 507 of Vol. I. (1881) 

 we gave an account of a careful study of diatoms from the 

 tolerably hard diatom-rock of Nykjobing in Jutland, made by 

 W. Prinz from transverse sections of three species : — Coscinodiscus 

 ocuhis-iridis, C. excentricus, and Trinacria regina. In the first two 

 instances he obtained exceedingly good demonstrations of the encasing 

 of one valve in the other, as also of the various thickness of the valves 

 at different places. In C. oculus-iridis he found the hexagonal honey- 

 comb-like meshes to have an opening at the base, the inner cell-layer 

 having a circular perforation in the middle of each cell. In Trinacria 

 regina he found the small round dots which cover the entire valve to 

 correspond to canals which completely perforate the thickness of the 

 valve. Whether this is so also in C. excentricus could not be deter- 

 mined with certainty, in consequence of the minuteness of the dots. 



Prinz's observations differ from those of Fliigel, 0. Miiller, and 

 Green to this extent, that these latter did not observe an actual per- 

 foration of the inner layer of the valve, by which the cell-contents 

 might altogether pass out. 0. Miiller's observations on Triceratium 

 Favm were founded on an ingenious method of flooding. In this 

 species and its allies, including Biddulphia reticulata, the inner layer 

 of the valve is completely covered by radial rows of fine dots, which are 

 nowhere wanting, and which exclude the presence of larger openings. 



It might be assumed that these small dots correspond to canals 

 which perforate the inner layer; but A. Grunow states* that he 

 has examined very large specimens of the variety sexangularis of 

 this species, in which this layer was so thick that it was possible, by 

 focussing, to detect the radiating dots on the inner side, and on the 

 outer side irregularly disposed short spines at the base of the honey- 

 comb-like cells, the walls of which were thickened above and some- 

 times elongated into a spine at the corners. Similar structures occur 

 in Triceratium Favus and in Coscinodiscus, while T. consimile Green, 

 which closely resembles the former, has exactly the structure of 

 C. oculus-iridis. In the last-named species a circular depression is 

 found in the inner layer of the valve, but no perforation. At these 

 depressions the valve is very thin, so that it may be completely 

 broken through there by boiling or in other ways. But an " incontro- 

 vertible proof " that there is no actual perforation is afforded by the 

 closely allied species C. Asteromphalus, connected with it by inter- 



* Bot. Ceutralbl., viii. (1881) p. 354. 



