58 



NATURE 



[November 9, 191 1 



between England and France, both before and after the 

 in.-tin period of glaciation. 



Dr. C. v.. Mos*; thought it a mistake to confine attention 

 to the local " Liisitanian " species of west Ireland and 

 south-west luigland. Hiloiiging to the same distributional 

 type are a nunitxr of halophytes, e.g. Limonium relicti- 

 latum, Suacda jruticosa, &c., which in Britain are limited 

 to the south and oast coasts. These probably migrated 

 from south Murope to Britain via the west coast of France. 

 Being salt-marsh plants, their seeds are probably carried 

 by ocean drifts. This may explain their absence from the 

 west coast of Britain, as the trend of the currents is in 

 an easterly direction. 



Mr. G. Claridge Druce contributed to the discussion a 

 statement of the appearance of species in isolated spots, 

 e.g. Scirpus maritimus in Berkshire, and suggested that 

 these were examples of chance dispersal by wind or birds. 

 The same was probably true of the rapid spread of Crepis 

 tara.\acifolia over Midland England during the last twenty 

 years. 



-Mr. Clement Reid briefly replied, and still adhered to 

 his main contentions. With regard to the possible survival 

 of plants in Britain, not only was the land itself glaciated, 

 but the surrounding sea was intensely cold. On the sub- 

 ject of post-glacial connections with the Continent we 

 cannot speak with absolute certainty, but he could find no 

 evidence of sufficiently great oscillations of level to allow 

 of their existence. The Irish peat-bog mammals referred 

 to by Dr. Scharff are all good swimmers, and could quite 

 well have crossed a narrow strait. This concluded one of 

 the best discussions which has been held under the auspices 

 of Section K. 



The Principles of Constructing Phytogeographical Maps. 

 A second discussion was arranged for Tuesday morning, 

 .September 5, on the principles of constructing phytogeo- 

 graphical maps. 



Dr. C. E. Moss, who opened this discussion, briefly 

 traced the history of the recently issued British vegetation 

 maps, and compared them with those produced on the 

 Continent. Dr. Moss pointed out the uses, and also the 

 limitations, of such maps. He emphasised the fact that 

 vegetation maps are just as important as geological maps. 

 Yet the latter are prepared and published by a Government 

 department, while the former are left to the initiative of 

 private individuals, who at present experience great 

 difficulty in securing the publication of their work. 



Prof. C. Schroter, who exhibited a fine collection of 

 phytogeographical maps he had brought with him from 

 Switzerland, classified such maps as follows : — (i) auto- 

 chorological maps, which show the distribution of 

 systematic units (genera, species, &c.) ; (2) synchorological 

 or formation maps, illustrating the distribution of plant 

 formations ; (3) epiontological or historical maps, giving 

 the distribution of floral elements and the history of their 

 innnigration ; and (4) floristic maps, showing the division 

 of a country into botanical regions. 



r^rof. O. Drude laid down certain important principles 

 which should be observed in constructing phytogeographical 

 maps. E.g. the colour scheme should be such as not to 

 Interfere with the general topography, which should be 

 ■clearly distinguishable even in vegetation maps. Prof. 

 Drude then proceeded to criticise the British maps in 

 respect to certain technical details. He was followed bv 



Mr. A. G. Tansley, who pointed out that most of Prof. 

 Drude's criticisms had been anticipated by the committee 

 for the survey and study of British vegetation. Many 

 improvements had been adopted in the later maps which, 

 as Dr. Moss had pointed out, still awaited publication. 



Dr. E. Rijbel distributed copies of his vegetation map of 

 the Bernina district in the Engadine. This map shows 

 what can be done in the way of indicating on a single map 

 such things as, e.g. in the case of woodland, not only the 

 distribution of forest, but also the proportion of the more 

 important trees, the types of undergrowth, &c. 



Ecological Papers. 

 Thursday was largely devoted to individual ecological 

 papers. 



Prof. F. W. Oliver, F.R.S.. read a paper on the life- 

 history of a shingle bank, in which he dealt with the con- 

 ditions under which plants exist on maritime shingle 

 NO. 2193, VOL. 88] 



beaches. Most shingle banks are very mobile. This is due 

 partly to the action of storm waves and partly to under- 

 mining by percolating sea water. .\ passive condition is 

 indicated by the presence of lichens, &:c. The origin of the 

 soil occupying the interstices of the shingle was discussed. 

 The most important source of this appears to be the drift 

 on the lee side of the bank. This gradually becomes in- 

 corporated with the shingle during the slow landward 

 march of the latter. Considered as a plant habitat, a very 

 remarkable feature of a shingle bank is the rich supply of 

 water with which it is provided, even in its upper zon<- 

 This feature requires further investigation. 



Prof. C. .Schroter next gave an illustrated account of t 

 Swiss National Park and its flora. There are in Switz 

 land at the present time four organisations working ( 

 the preservation of natural and prehistoric monuini.:- 

 One of the results of this movement has been the c^t ■ li-:i- 

 ing of a National Park, or reservation. This is planii"! 

 to cover an area of 200 square kilometres, about 90 <( 

 which have already been acquired. | 



Prof. J. Massart, in a very interesting paper on phyio- I 

 geography as an experimental science, strongly urged th** \ 

 necessity for experiment as a method of attacking probl* " 

 of plant geography. One example mentioned was the ( . 

 of certain moorland plants (e.g. Calluna vulgaris) \\h 

 flourish in such an unusual habitat as the limestone p.iN 

 ments of west Ireland. Why are these calcifuge spe( 

 able to grow on limestone in Ireland? Is it because ; 

 climate is sufficiently favourable to enable them to wii 

 stand the deleterious effects of the calcareous soil? <» 

 because the limestone forms of these species are bioloL; ■ 

 races, analogous to the cases of some parasitic fungi ? ' 

 is it that certain competing species are absent fr 

 Ireland? This and many similar problems can only 

 solved by direct experiment. 



The afternoon session was opened by Prof. H. < 

 Cowles, who gave an illustrated account of a fifteen-y. 

 study of the advancing sand-dunes of Lake Michig. 

 These dunes are frequently 65 metres in height, and trn 

 so rapidly that few of the antecedent plants are able 

 survive. Curiously enough, those which do so are not 

 more xerophytic species, but swamp plants and mesophyt 

 such as Cornus, Salix, Populus, &c. The survival of th 

 plants depends on their capacity to elongate and prod, 

 new adventitious roots rapidly. 



Miss S. M. Baker, in describing the brown seaweed- 

 a salt marsh, stated that all the brown seaweeds occuri ; 

 near high-water level on rocky shores are capable of giving 

 rise to marsh forms. Such marsh forms are frequently 

 characterised by a spiral twisting of the thallus. 



Prof. R. H. Yapp next discussed the causes which deter- 

 mine the formation of hairs and palisade cells in plants. 

 The results of many previous experiments show that, iHt 

 general, palisade tissue and the hairs on aerial shoots are' 

 best developed under external conditions which either 

 favour transpiration or hinder absorption. The conclusion 

 was arrived at that the initial stimulus leading to th*» 

 development of these special cells is connected with .t 

 diminished water supply. But turgidity is a necessary cor- 

 dition for the actual growth of the cells. Thus peril 

 fluctuations in the turgor of the cells concerned, such 

 will frequently occur during the alternation of day .ii.d 

 night, may play an important part. 



Dr. F J. Lewis read a paper on the forest stages repre- 

 sented in the peat underlying the moorlands of Britain. 

 The author's earlier researches on this subject are well 

 known. In this paper he gave some of the results of his 

 more recent work in the Hebrides and elsewhere. The 

 paper was well illustrated by lantern-slides. 



.\ paper was communicated by Miss L. Baker and Mr. 

 B. W. Baker on the plant associations of the district round 

 Macclesfield. 



Mr. W. B. Crump, in an interesting paper on the water- 

 content of acidic peats, dealt with the question of the 

 water supply of plants growing on acid soils. Mr. Crump 

 emphasised the importance of considering the humus- as 

 well as the water-content when analysing these soils. He 

 contended that if the results of such analyses be expressed 

 bv the ratio water-content 'humus-content some indication 

 is obtained of the amount of water available for absorption 

 by the plant. 



