TRANSACTIONS OP SECTION K. 581 



TUESDAY, SEPTEMBER 5. 



The following Paper was read : — 

 The Balance-sheet of a Plant. By Dr. Francis Darwin, F.P.S. 



Discussion on the Principles of Constructing Phyto-cjeoqrapliical Maps. 



Dr. C. E. Moss, who opened the discussion, briefly traced the history of the 

 recently issued British vegetation maps. Those of Edinburgh and of Northern 

 Perthshire, by the late Robert Smith, were the first to be published ; and these 

 were a direct result of the inspiration which R. Smith received from Professor 

 Ch. Flahault, of Montpellier, who had previously published a vegetation map 

 of a portion of the South of France. Vegetation maps by Professor O. Drude, 

 of Dresden, and of Professor C. Schroter, of Zurich, were published about the 

 same time as that by Flahault; and since then many had been published by 

 Swiss, Austrian, and British botanists. 



The opener concluded his remarks by summarising the uses of vegetation 

 maps. In brief, vegetation maps are just as useful to the botanist and to the 

 nation as geological maps. Yet whilst geological maps are prepared and pub- 

 lished by a Government Department, the preparation of vegetation maps is left 

 to private individuals, who have no definite means of obtaining publication of 

 their work. At the present moment, there are as many completed British vegeta- 

 tion maps which cannot be published owing to lack of funds as there are of such 

 published maps. The time is approaching when it will be necessary to consider 

 whether or not the preparation and publication of British vegetation maps 

 should be placed on precisely the same footing as the preparation and publication 

 of geological maps. 



The following also contributed to the discussion : — 



Prof. C. Schroter (who exhibited a fine collection of phy to-geographical maps), 

 Prof. 0. Drude, Mr. A. G. Tansley, and Dr. E. Riibel. 



The following Papers were then read : — 



1. The Water-content of Acidic Peats. By W. B. Crump, M.A. 



Recent ecological researches all emphasise the importance of edaphic factors 

 in determining the distribution of plant associations, and the complete lack of 

 exact data based upon quantitative experimental work. While the nature of 

 the soil and the richness or poverty of the soil-water in nutrient salts are factors 

 of primary importance, the water-content would seem to be of equal importance. 

 As regards this soil-water it is recognised that some of it, possibly much of it in 

 acidic or saline soils, is not available to plants, so that the determination of 

 the available, or what Schimper has termed the physiological, water is also 

 desirable. The last point is considered in another paper ; the other factors are 

 eliminated by selecting a series of habitats exclusively on siliceous rocks with 

 the soil-water deficient in soluble salts, but always more or less acidic through 

 the presence of humus acids. As the alkaline peats differ in all these respects 

 and support totally different vegetation, their consideration is reserved. 



The peats examined were all obtained on the moorlands of the Southern 

 Pennines, and mostly in the neighbourhood of Halifax. The sample was 

 selected from the zone of active root absorption, and if not apparently homo- 

 geneous it was divided into layers. It was taken during dry weather — never 

 within a few days of any rainfall — with the purpose of obtaining the minimum 

 value. The water-content is exclusively the water that evaporates when the 

 peat is exposed to the air at or about 15° C., and the results are expressed in 

 terms of such air-dry peat. The peat was then oven-dried and subjected to 

 combustion to determine the humus and mineral residue. This not only graded 

 the peats, but eventually fnrnished the solution of the problem. Without a 



