March, 1902.] 



KNOWLEDGE. 



49 



ILLUSTRATED MAGAZINE 



~^EN€E JLiTERATyp^AB^ 



Founded by RICHARD A. PROCTOR. 

 Vol. XXV.] LONDON : MAECH, 1902. [No. 197. 



CONTENTS. 



^ PAOK 



Studies in the British Flora. II.— Notes on Plant 



Geography. Hy K. Lloyd 1'B.iKOKK, b.\. {Illustrated) 49 

 The Migrations of the Skylark and the Swallow, B.v 



IIarhy F. WiTiiKKHY, F.Z.3., m.h or 52 



Like and Yet Unlike: The Flying-Squirrels of Asia 



and Africa. Jiy K. Lydf.kker. {Plate) 51- 



The Lucid Stars. By ,T. E. Gobb, f.e.a.s. 50 



Astronomy without a Telescope. XI. — Morning and 



Evening Stars. Bv K. Walter Maunder, f.b.a.s. 



{Illt'xtratrd) ' 58 



The Use of Hand Telescopes in Astronomy. II. — The 



Sun. By Cecil Jacksok. {Illustrated) 60 



Letters • 



Tub Flight of a Hailstone. By Rev. AaTnrH East. 



{Illustrated) '. 61 



The Tsb of Hand Telescopes. By M. Habe. Note 

 hy E. Walter Mauhdeb 62 



\ Method of Gknebatinq .Vcettlese. By R. Knowles 62 

 British Ornithological Notes. Conducted by Habey F. 



Withseby, F.z.a., M.B.o.r 62 



Notes 62 



Notices of Books 04 



Books Rkcbivkd Go 



Wing-Links. By E. .\. Bitler, b.a , b.sc. {Illustrated) ... 65 

 Preserving and Mounting Rotifera. By Charles F. 



Rdi.-^.selet .' 68 



Microscopy. Conducted by M. I. Cross 68 



Notes on Comets and Meteors. By W. F. Denning, 



F.R.A.S 70 



The Face of the Sky for March. By W. Shackleton, 



F.R.A.3. 70 



Chess Column. By C. U. Locock, b.a 71 



STUDIES IN THE BRITISH FLORA. 



By R. Lloyd Praeger, b.a. 

 II. -NOTES ON PLANT aEOGKAPHY. 



It is A matter of ever^-day observation that the flora of 

 two udjoiniiig districts is never in all respects identical. 

 Even if we carefully list the plants growintj in one 

 nieado'.'?, and compaie it witli the flora of an adjoining,' one, 

 which, iu respect of size, situation, soil and moisture 

 appears precisely similarly situated, a certain diversity 

 will be found. This arises from the fact that plants are 

 so nicely adjusted to particular conditions of light, tem- 

 perature, moisture and soil, that differences of these, 

 almost inappreciable to our observation, will produce a 

 slight balance in favour of one species as compared with 

 another. In our meadow the ground is already densely 

 overcrowded with plants, all of which have through long 

 competition with their neighbours seized on every device 

 and habit that will aid tiiem in the struggle, and have 

 established by force of arms their right to live. Thev all 

 grow, so to speak, under high pressure, and the least 

 change of outward conditions which tells in favour of one 

 species is taken advantage of, and the less adapted plant 



goes under. So we can understand that any area of 

 natural vegetation displays a complicated adjustment as 

 regards its composition, and that the distribution of the 

 component s]iecics is tlio inevitable result of a complex 

 set of conditions, not the effect of chance. 



In limited areas, moisture is the dominant factor of 

 environment which determines the nature of the flora. 

 If one meadow is marshy and another dry, a greater 

 change of flora is produced bv this variation than would 

 result from any other physical difference. Soil is probably 

 the ne.\t most important factor. When we come to deal 

 with larger areas, climate begins to assume importance, 

 till at length, in surveying the vegetation of the globe, we 

 find climate the grand doiuiaatiug iuHuem-e which gives 

 to countries and to continents their floral characteristics. 



Of the four great Zones of Heat — Torrid or Inter- 

 tropical, Warm-temperate, Cool-temperate, and Ai'ctic- 

 Alpine or Frigid— into which the earth's surface has been 

 divided, our Islands lie in the Cool-temperate, with certain 

 mountain-tops rising into the Arctic -Alpine. The general 

 floral characteristics of this zone are the number of 

 deciduous trees in proportion to evergreens, the number of 

 herbaceous jilants in proportion to trees, the gregarious 

 or social character of many of the trees and shrubs, such 

 as Pine, Oak, Gorse, Heather, which form vast colonies ; 

 and the abundance of greensward-producing grasses, and 

 of terrestrial mosses and foliaceous lichens. Compared 

 with the Tropics, we see in the increase of herbaceous 

 plants and of deciduous trees, and of hardy low-growing 

 plants of all kinds, adaptation for the successful weather- 

 ing of our winter, a climatic change unknown in the 

 Tropics. As compared with the vegetation of the Arctic- 

 Alpine zone, the Cool-temperate zone is remarkable for 

 its forest-trees, which are unsuited for the long, cold, 

 stormy winters of high latitudes, and for its abundant 

 annual plants, which under arctic conditions would not 

 find, during the brief summer, a warm period sufficient for 

 their growth, flowering and ripening of seed. 



To the character of mir climate and vegetation we owe 

 one of the most delightful features of these countries. On 

 account of the cessation of vegetative growth during our 

 winter, the plants, unlike those of the Tropics, have to 

 compress their jieriod of flowering into a few summer 

 months ; and it is this, coupled with the gregarious or 

 social character of the flora, that gives us our lovely 

 English fields of Buttercups aud Daisies, our glorious 

 sheets of Golden Gorse and Purple Heather, whic^ we 

 would iu vain attempt to match amid the heavy luxuriance 

 of tropical vegetation. 



While our British flora is thus relegated in toto to one 

 of the great climatic floral divisions of the world, it is yet 

 by no means homogeneous in character. Great Britain 

 extends over some 700 miles north and south, a range 

 of latitude sufficient to produce a considerable contrast 

 l)etween the flora of its opposite limits. A difference iu 

 annual temperature of over five degrees Fahrenheit exists 

 between Caithness and Cornwall. But the actual conditions 

 of temperature under which the British flora exists is far 

 more varied than this. The requirements of a plant, as 

 regards temperature, includes two important factors. It 

 must have heat enough during summer to mature its seed, 

 and the w'inter temperature must not be so low as to 

 injure its tissues. The natural limits of a plant's range 

 are usually fixed by one or other of these conditions, 

 according as the constitution of the plaut renders the 

 ([uestion of summer maximum or winter minimum 

 temperature the more important to it. The presence of 

 large land areas conduces to a wide range of annual 

 temperature — hot summers and cold winters — aud in 

 continental areas, therefore, the former class — heat-lovers, 



