02 PROCEEDINGS OF SOCIETIES. 



elected Associates. — Mr. B. Daydon Jackson exhibited a complete 

 series of the various editions of Dillenius's ' Historia Muscorum,' 

 Oxford, 1741, and its reprint, Edinburgh, 1811, in illustration of 

 tbe following communication, The Eev. J. M. Crombie read a 

 paper "On the Lichens of Dillenius ('Historia Muscorum'), as 

 illustrated by his Herbarium." The latter collection is preserved 

 in the Botanic Gardens at Oxford; and the specimens, though 

 well-nigh 150 years old, are still in a good state of preservation. 

 The earlier writers on Cryptogamic Botany in their synonymy and 

 nomenclature made constant reference to his descriptions, hence 

 the present importance and value of an analysis of his material, 

 and tbe more so as hitherto no systematic examination has been 

 attempted, though some old writers have compared a few forms. 

 Notwithstanding very considerable accuracy of identification of the 

 Dillenian Lichens, serious mistakes appear to have crept in. 

 Mr. Crombie reviewed the series, giving a conspectus and technical 

 data adapted to the present standpoint of Botany. 



Geologists' Association. 



January 2, 1880.— Mr. G. S. Boulger read a paper on " The 

 Geological and other causes of the distribution of the British Flora," 

 of which the following is an abstract :— Geographical Botany dates 

 from Humboldt's invention of isotherms and altitudes. Since his 

 time we have been indebted to Meyen, Schouw, Watson, Edward 

 Forbes, Tburmann, DeCandolle, Grisebach, and, for a natural 

 system of distribution, more especially to Sir Joseph Hooker and 

 Mr. Bentham. The causes of distribution may be divided into 

 three heads : genetic or original, means of dispersal, and checks to 

 dispersal or causes of survival within a limited area. The chief 

 means oi dispersal are birds, ocean currents, rivers, wind, man, 

 and hairy or woolly quadrupeds. The checks to dispersal may be 

 classed as barriers, $.#., oceans, deserts or mountain -chains, 

 climate soil, watersheds, and the struggle for existence with pre- 

 established forms ; climate consists chiefly in temperature and 

 humidity and is by far the chief physical (as opposed to genetic) 

 cause of distribution ; temperature depends on latitude, proximity 

 to the ocean, and altitude. Climates form two distinct classes, 

 continental and insular, the latter being moister and more uniform, 

 J.«n bave a less hiberno-aestival variation— The west coast of 

 l»ritam, for example, is more insular in climate than the east.— 

 ineir native climate is as clearly reflected in the vegetative system 

 of plants as m their method of fertilisation in the reproductive 

 organs, boils affect distribution mainly by their differences of 

 texture and consequent permeability, but also by their chemical 

 composition, especially by the presence or absence of lime. 

 Waters!* affect distribution in that plants are mainly carried 



t'Z/™™' ii : i , (1 ' tU ? gh perll:, l ,s « a S enc y of secondary 

 nipoitance, are the mos available of all natural bases of mapping", 



ufiFZPF** 0{ueiil }y exact circumscription. Analyzing the 

 lbOO British flowering plants, we find 20 confined to the Channel 



