ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 195 



tion of the different methods of investigation — by means of the air-pump, 

 &c. The results of the experiments are then detailed ; the permeability 

 of dry and damp cell-walls under reduced and increased atmospheric 

 pressure. The cell-wall is even more pervious in the damp than in the 

 dry state. The dry moss-cell contains very little air owing to the strong 

 contraction of the walls when dry. It is difficult to explain the rapid 

 extrusion of air and infiltration of water into the active sporangial cells 

 of ferns and Selaginella. In the leaves of Milium only a portion of the 

 membrane of each cell is permeable — probably the upper and lower tan- 

 gential walls ; the other parts resist a pressure of several atmospheres. 



Ferns and Fern Allies of North America.*— W. R. Maxon has 

 compiled a list of the vascular cryptogams of North America north of 

 Mexico, with their principal synonyms and geographical distribution. 

 The list comprises 280 species, 20 varieties, and a hybrid, and is based 

 on an examination of the national herbaria and the principal private 

 collections of the country. An account is given of the only two 

 standard treatises, by D. C. Eaton and L. M. Underwood respectively, 

 which cover the whole of the vast territory under notice ; and this is 

 followed by a chronological bibliography of the principal papers and 

 lists that bear upon the subject. 



L. M. Underwood f publishes a severe criticism of Hooker's Synopsis 

 Filicum with special reference to the genus Gymnogramme, which he 

 shows to comprise fragments of several generic groups in no way related 

 to one another save in the absence of an involucre. Some are related 

 to the Polypodieae, some to the Aspidieae, one possibly to the Vittariese, 

 and others to the Asplenieas. It is as great an error to transfer them 

 bodily to the Pterideae as is done in Die naturlichen Pflanzenfamilien. 

 The name Gymnogramma may have to give way to the earlier name 

 Gymnopteris. Only two of the species occur in the United States, and 

 they belong to two distinct genera Ceropteris and Bommeria, and to the 

 former of these is now added another species from California. 



The same author % supplies a preliminary review of the genus Daiwa, 

 with a synopsis of twelve North American species, among which are five 

 new. 



Equisetum hyemale.§ — A. Bennett records and discusses! the dis- 

 tribution of Equisetum hyemale in Scotland, Scandinavia, and North 

 America. 



Mosses. 



European Harpidia.|| — C. Warnstorf publishes a detailed study 

 of the difficult section of the genus Hypnum, usually known as the 

 Harpidium group. Aquatic in habit, the species are extremely variable 

 and well-nigh impossible to define. After summarising the various 

 schemes of classifying the group which have been put forward by Sanio, 

 Renauld, Klinggraeff, and Limpricht, the author gives a list of the col- 

 lections which he has examined and proceeds to unfold his own views, 



* Proc. U.S. Nat. Museum, xxiii. (1901) pp. 619-51. 



t Bull. Torrey Bot. Club, xxix. (1902) pp. 617-34. 



% Tom. cit., pp. 669-79. § Ann. of Scottish Nat. Hist., 1903, pp. 47-8. 



U Beih. z. Bot. Centralbl., xiii. (1903) pp. 388-430 (2 pis.). 



O 2 



