November 29, 1894] 



NATURE 



119 



dependent not only on latitude, but largely on configuration of 

 the land, and especially on the direction of moisture-bearing 

 winds with reference to the trend of mountains. 



The winds from the Pacific Ocean striking against the coast 

 range are forced by the expansion and consequent cooling to 

 give up much of their moisture on the windward side ; a 

 second impact and further condensation of the moisture 

 takes place on the Cascade range and Sierra Nevada. On 

 descending, with consequent compression, the wind becomes 

 warmer and drier, so that the interior basin, without additional 

 sources of moisture and no additional cause for condensation, is 

 left without much rainfall and with a very low relative 

 humidity, namely, below 50 per cent. The Rocky Mountains 

 finally squeeze out whatever moisture remains in the air 

 currents, which arrive proportionally drier on the eastern slope. 

 This dry condition extends over the plains until the moist 

 currents from the Gulf of Mexico modify it. Somewhat 

 corresponding, yet not quite, to this distribution of moisture, 

 the western slopes are found to be better wooded than the 

 eastern, and the greater difficulty of establishing a forest cover 

 here must be admitted ; yet since the forest has the capacity of 

 creating its own conditions of existence by increasing the most 

 important factor of its life, the relative humidity, the extension 

 of the same may only be a question of time. 



Temperature extremes, to be sure, also set a limit to tree 

 growth, and hence tl G so-called timber line of high mountains, 

 which changes in altitude according to the latitude. 



If now we turn our attention from the phyto- topographic 

 consideration of the forest cover to the phyto-geographic and 

 botanical features, we may claim that the North American 

 forest, with 425 or more arborescent species, belonging to 158 

 genera, many of which are truly endemic, surpasses in variety of 

 useful species and magnificent development any other forest of 

 the temperature zone, Japan hardly excepted. In addition there 

 are piobably nowhere to be seen such extensive fields of distri- 

 bution of single species. 



These two facts are probably explained by the north-and- 

 south direction of the mountain ranges, which permitted a re- 

 establishment after the Ice Age of many species farther north- 

 ward, while in Europe and the main part of Asia the east-west 

 direction of the mountains offered an effectual barrier to such 

 re-establishment, and reduced the number of species and their 

 field of distribution ; nor are the climatic diflferences of different 

 latitudes in North America as great as in Europe, which again 

 predicates greater extents in the fields of distribution north and 

 south. On the other hand, the dilferences east and west in 

 floral composition of the American forest are greater than if an 

 ocean had separated the two parts instead of the prairie and 

 plains. This fact would militate against our theory ihat the 

 intermediate forestless region was or would be eventually 

 forested with species from both the established forest regions, 

 if we did not find some species represented in both regions and 

 a junction of the two floras in the very region of the forestless 

 areas. 



{To be continued.) 



SOCIETIES AND ACADEMIES. 



London. 



Zoological Society, November 20. — Sir W. H. Flower, 

 K.C.B., F.K.S., President, in the chair. — Mr. F. G. Parsons 

 read a paper on the anatomy of Athcrttra africaua^ compared 

 with that of other porcupines. In addition to the points men- 

 tioned by Drs. Gray and Giinther, as differences between the 

 skulls of A. africaiui and A. niaciiira, the arrangement of the 

 fronto-nasal suture, the position of the maxillo-malar suture, 

 and the frequent presence of an " »j anti-epilepticum" were 

 noticed. — A communication from Mr. J. T. Cunningham 

 treated of the significance of diagnostic characters in the 

 Pleuronectidie. — Mr. A. Smith Woodward read a description 

 of the so-called Salmonoid fishes of the English Chalk, dealing 

 with the osteology of OsmtroiJes Icioesicnsis, Elopopsis crassiis, 

 and Aiilolepis typiis. — Mr. W. Garstang read a paper on the 

 Gastropod Colpodaspis pusilla of Michael Sars. lie described 

 a specimen of this rare moUusk found by him at Plymouth 

 in the early part of the year. — A communication from Mr. 

 A. D. Bartlelt gave an account of the recent occurrence 

 in the Society's menagerie of a case of one boa swallowing 



another of nearly equal size.— A communication from Prof. R. 

 Collett contained a description of a new Agonoid fish from 

 Kamtschatka, proposed to be called Agoiius gilberli. 



Royal Meteorological Society, November 21. — Mr. R. 

 Inwards, President, in the chair.— Dr. H. B. Guppy read a 

 paper on suggestions as to the methods of determining the 

 influence of springs on the temperature of a river as illustrated 

 by the Thames and its tributaries. The methods suggested 

 were (l) comparison of the curves of the monthly means of the 

 temperatures of the air and of the water for the river under 

 observation with those of a river beyond the controlling 

 influence of springs ; (2) comparison of the monthly means of 

 the temperature of the river under investigation with that of a 

 river beyond the control of the springs ; (3) comparison of the 

 range of the monthly means of the river temperature with that 

 of the air in the shade ; (4) comparison of the daily range of 

 water temperature at different stations along a river's course ; 

 (5) comparison of sunrise observations made at different 

 stations along a river's course ; (6) comparison of observations 

 made at difterent stations along a river's course at the hour of 

 maximum temperature ; (7) comparison of the results obtained 

 from a single series of observations made in one day along the 

 whole course of a small tributary like the Wandle, or along the 

 upper course of a larger tributary as the Kennet ; and (8) deter- 

 mination of the distance from its sources at which the river begins 

 to freeze. — Mr. Eric S. Bruce exhibited and described some 

 lantern slides showing the disastrous effects of the great gale of 

 November 17 and 18, 1893, upon trees in Perthshire, Scotland. — 

 Mr. Alfred B. AYollaston gave an account of the formation of 

 some water-spouts which he had observed in the Bay of Bengal. 



Cambridge. 



Philosophical Society, November 12. — Prof. J. J. Thomson, 

 President, in the chair.— On the inadequacy of "the cell theory 

 and on the development of nerves, by Mr. A. Sedgwick. The 

 I author pointed out that the cell-theory, in so far as it implied that 

 j the organism was composed of cell-units derived by division 

 from a single primitive cell-unit, the ovicell, would not bear the 

 scrutiny of modern embryology, and that in fixing men's 

 attention too much upon the cell as a unit of structure, it had 

 had a retarding influence on the progress of the knowledge of 

 structure. He illustrated this latter point by reference to the 

 current ideas on two important subjects : the structure of the 

 embryonic tissue called mesenchyme, and the development of 

 nerves. The mesenchyme is not composed of separate branched 

 cells, but has rather a spongy or reticulate structure, and is 

 continuous both with ectoderm and endoderm. Nerves do 

 not develop as outgrowths of the central organ, but arise in 

 situ from the mesenchyme. — Note on the evolution of gas by 

 water-plants, by Mr. F. Darwin. 



Paris. 

 Academy of Sciences, November 19. — M. Lcewy in the 

 chair. — After the reading of \.\i& prods verbal, the meeting was 

 adjourned as a mark of respect to the late Czar of Russia. 



Amsterdam. 



Royal Academy of Sciences, October 27.^Prof. Van de 

 Sande Bakhuyzenin the chair. — Mr. Franchimont, in presenting 

 Mr. H. van Erp's thesis for the Doctorate in Chemistry at the 

 University of Leyden, entitled " Studie ober ahphatische 

 nitraminen," described it as a summary of all the known acid 

 and neutral nitramines and nitramides, and also of their modes 

 of formation. In dealing with the action of water, acids and 

 alkalies on these bodies, Sir. van Erp considers them as derived 

 from the amide of nitric acid, and compares them to the analogous 

 derivatives of nitrous acid, hypochlorous acid, &c. For ex- 

 perimental purposes he made the unknown butyl- and hexyl- 

 derivatives ; nine urethanes, seven nitro-urethanes, four acid 

 nitramines with several salts, two mixed neutral nitramines. He 

 failed, however, to obtain nitro-compounds of the tertiary butyl 

 amidoformates. He has observed that while the potassium 

 salts of the acid nitramines yield the neutral methyl-derivatives 

 hy the action of melhyliodide, the silver salts produce an 

 isomeric methylated nitramine, or a mixture of the two. Similar 

 observations in the case of the salts of phenylnitramine were 

 made later by Bamberger. The behaviour of acid nitramines 

 lowards dilute sulphuric acid was studied on hexylnitramine, 

 the result being N^O, two hexanoles, a primary and a secondary 



NO. 1309, VOL. 51] 



