438 



kxowli:dge. 



Novr.MISER, 1911. 



Deimos are 1877-7, 1879-9, 1886-2. 1892-6. 1894-8. 1896-9. 

 1907-5. For Phobos 1877-7, 1879-9, 1892-6, 1894-7, 1894-8. 

 1896-9. 1907-5. 



BOTANY. 



By Professor F. Cavers, D.Sc. F.L.S. 



PAPERS OX ECOLOGY.— Two of the Continental 

 botanists contributed papers, both on Ecology. Prof. Schroter 

 described in an interesting fashion " The Swiss National Park 

 and its Flora," giving an account of the admirable and 

 extensive operations of local Committees, assisted by the 

 Federal Government, in the useful worU of conserving the 

 natural features of various parts of Switzerland and protecting 

 the native flora from extinction. Prof. Massart described, 

 under the title " Phytogeography as an Experimental Science," 

 various methods and results of experiments in which plants 

 were grown under conditions strikingly different from their 

 natural habitats. 



Professor Cowles described his observations on advancing 

 sand-dunes in Michigan, which he has studied for about fifteen 

 years. The dunes are of gigantic size, the advancing front 

 having an altitude of twenty-five to sixty-five metres abo\e the 

 country in the path of advance. So high are the dunes and 

 so great their rapidity of movement, that very few of the 

 overtaken plants are able to survive. Curiously, the plants 

 able to endure partial burial by these dunes are not xerophytes. 

 like the pines and oaks, but swamp plants and mesophytes. 

 such as species of Sirlix (Willowt, Popiihis (Poplar), and 

 Coniiis : the shrubby plants are stimulated by the advance 

 of the sand to extraordinary elongation of their stems. 

 Survival depends upon the capacity of a plant to put forth 

 new roots and to elongate as rapidly as the dune advances. 

 In some places there are Elms thirty metres in height, above 

 the original countr\- level, with the tree tops projecting only 

 one or two metres above the sand, yet their foliage is healthy 

 and they flower and fruit vigorously. 



Miss Sarah Baker, dealing with '" The Brown Seaweeds of a 

 Salt Marsh," stated that the capability of giving rise to marsh 

 forms seems to be shared by all the brown seaweeds inhabit- 

 ing the upper parts of rocky shores. Pclvctia canalicnlata, 

 Fiicus spiralis. Ascophyllnin nodosunu and Fiiciis 

 vcsicitlosiis. all show marsh varieties or species. The reason 

 that FitcHs serratns and F. ccmnoides have no representa- 

 tives in the marsh habitat is probably their intolerance of 

 desiccation. The physical and chemical environment factors 

 on the marsh being much more complex and varied than on a 

 rocky shore, one would expect a corresponding variation in 

 the structure of its plants. The most marked characteristics 

 of the common marsh species are a great tendency to spiral 

 twisting or curling of the thallus— and vegetative reproduction. 

 That this latter feature is not directly caused by the marsh 

 habitat is show^i by exceptional species where reproduction is 

 normal. The zoning between the brown seaweeds of a marsh 

 is often very striking ; but the factors governing it must be far 

 more complicated than those operating on the seashore. 

 The extensive mattings of brown seaweeds often found on 

 English marshes have a decidedly beneficial effect on the 

 Phanerogams. It seems possible that F. vuliibilis may act 

 as a pioneer in the establishment of salt marshes in certain 

 cases. 



Mr. W. B. Crump contributed two interesting and detailed 

 papers on " The Water Content of Acidic Peats " and " The 

 Wilting of Moorland Plants." These two papers, somewhat 

 too lengthy to be reproduced here, and too condensed to be 

 readily summarised, represent an earnest attempt to fill a 

 decided gap in ecological literature and to supply exact data, 

 based on quantitative experimental work, regarding the water- 

 content, humus content, and mineral content of the soil on 

 moorlands, and the percentages of available soil-water for 

 different plants. Much work of a similar kind has been done 

 with arable soils, but it is important to have as much know- 

 ledge as possible concerning the physical and chemical 



characters of economically barren soils, in order to be able to 

 deal better with the problems of plant distribution. 



Miss Lilian Baker and Mr. B. W. Baker, contributed a paper 

 entitled "Types of Vegetation in the District around Maccles- 

 field." The area under study comprises parts of Cheshire and 

 Staffordshire, the four corners being roughly represented by 

 the towns of Northwich. Crewe, Leek, and Macclesfield. It 

 includes part of 111 the Cheshire Plain, largely cultivated, with 

 numerous parks and wooded estates, and a few sandy heaths 

 and "mosses": and 121 the Pennine Foothills consisting of 

 approximately parallel ridges intersected by the Dane valley 

 and other wooded ravines and covered by moors. The rain- 

 fall increases from the level western parts towards the hilly 

 east The two regions show marked geological differences ; 

 the plain consists of triassic rocks buried in Pleistocene times 

 under a thick covering of glacial deposits, while the hill region 

 consists of carboniferous rocks. Peat-mosses occur on the 

 plain in the position of former glacial lakes, but have been 

 largely reclaimed. The chief Associations described are (II 

 Moorland and Heath ; (2) Grassland, represented by heath 

 pastures; (3! Woodland; (4) Aquatic, and (51 Pasturage. 



Prof. Oliver gave an account of " The Life History of a 

 Pebble Beach," and Prof. Vapp discussed " The Causes of the 

 Formation of Hairs and Palisade Cells in certain Plants," 

 but no printed resume is available in either case ; probably 

 the results will be published in botanical periodicals sooner or 

 later, when they will be noted here. The same remark applies 

 to a paper read by Dr. F. J . Lewis on " The Forest Stages 

 represented in the Peat underlying the Moorlands of Great 

 Britain." 



Some interesting points were raised by Mr. C. Reid, in his 

 paper on " The Relation of the Present Plant Population of the 

 British Isles to the Glacial Period." A century ago it was 

 generally supposed that species had originated mainly in the 

 districts in which they were then found ; but this presented the 

 obvious difficulty that the same species was not likely to have 

 originated at several different points, hence the anomalies of 

 discontinuous distribution were left unexplained, and with the 

 growth of the idea of evolution it was realised that faunas 

 and floras had a past history, even if the included species had 

 remained unchanged, and botanists realised that there were 

 many further points requiring explanation. For instance, it 

 was early noticed that each of our mountain tops possessed a 

 small outlying fragment of the arctic flora ; how, then, came 

 it that the same species occupied so many difterent mountains? 

 About sixty years ago, Edward Forbes seized the clue afforded 

 by the discovery of the Glacial Period, and explained the 

 arctic plants stranded on our mountain tops as relics of this 

 Period — they were left behind when the climate became too 

 warm for them to survive longer on the plains, and the 

 subsequent discovery of fossil remains of these plants scattered 

 over the plains, often associated with relics of arctic animals 

 now extinct in Britain, seemed a brilliant proof of Forbes' 

 view, which has been generally adopted. 



But Forbes' hypothesis, granting that it explains our alpine 

 flora, makes more difficult, rather than easier, the explanation 

 of our southern flora, which occurs in a similar way. stranded 

 in some of the warmest low-lying parts of Britain. This 

 difficulty appears to have been generally overlooked. We 

 must start with the assumption that we have merely to account 

 for the incoming of our existing flora, after an eai'lier (Pre- 

 glaciall assemblage had been swept away as completely and 

 effectually as the celebrated volcanic eruption wiped out the 

 plants of Krakatoa. None of our flowering plants, excepting 

 a few arctic and alpine species, could possibly have survived 

 and lived through the cold of the Glacial Period. We know- 

 that the same temperate species that live in Britain now were 

 here in pre- Glacial times, hence they must have found a 

 refuge somewhere, but this refuge cannot have been in Britain. 

 During the greatest intensity of the cold all Scotland, Ireland, 

 and the greater part of England were buried under ice and 

 snow, except possibly for some high peaks on which a few- 

 arctic species survived; ice filled the North Sea and covered 

 the lowlands of England down to the mouth of the Thames, 

 its southern limit extending to South Wales, where tongues of 



