Nov. 30, 1883. 



♦ KNOWLEDGE ♦ 



m^ MAGAZINE OF^GIENCE^ 



y UmuyORDED -£XACTIJDESCRIBED .: 



LONDON.- FRIDAY, NOV. 30, 1883. 



Contents op No. 109. 



PAQB 



A Natnralist'B Tear : The Eeipi of 

 Evergreens. By Grant Allen ... 327 



The Zone of Small Planets. By 

 B. A. Proctor 328 



Sea Anemones. The Dahlia. {Con- 

 tinued ) By Thomas Kimber 329 



TheOccupationsof the People. Bv 

 Percy Russell '.. 3*) 



Tricycles in 1883. By J. Browning 332 

 Monster. By R. A. 



The Amateur Electr 



(/««,.) 



Pons' Comet. {Hint.) ; 



Reviews ; Evolution and Natural 

 Theology. By ?rdward Clodd t 



A Challenge from ihe Earth-Flat- 

 tening Society. Bt R. A. Proc 



Ifa 

 Proctor. 



Correspondenc 

 Measuremen 



Ordn 

 -Storn 



Map 

 1 Glass, .iu. 337 



A NATURALIST'S YEAR. 



By Grant Allen. 



THE KEIGN OF EVERGREENS. 



fl^HE poor stripped and draggled garden is beginning to 

 \_ look very bare now of all excpt a few straggling 

 iate-flowering shrubs and those trusty adopted friends that 

 we have always with us, the shrubby, large-leaved soutliern 

 evergreens. In northern climates, we must ruefully admit, 

 there are hardly any true evergreens, save only the 

 conifers, with their stiff and needle-like foliage, such as 

 pines and spruce-firs ; but we make up for it to some 

 extent by borrowing from warmer or more southern lands 

 the laurels, aucubas, laurustinuses, and rhododendrons that 

 help to keep bright our English lawns and shrubberies 

 throughout the long and weary winter months. Indeed, 

 our only native flat-leaved shrubs that retain their full 

 ;j;reenness from year's end to year's end are privet, box, 

 and butcher's broom, all three of them very doubtfully 

 indigenous to these islands. It is the rule with English 

 trees and shrubs to shed their foliage every autumn ; and 

 the fashion in which they do so shows very clearly how 

 purposive and well-adapted to their conditions in life is the 

 deciduous habit For the leaves do not merely tumble off 

 anyhow, casually, before the first fierce autumnal wind ; 

 if they did so there would be loss of .sap and of valu- 

 able foodstuffs to the whole plant of whose joint 

 ooramonwealth they form the partially independent mem- 

 bers : their fall is duly provided for beforehand, and 

 when at last it actually takes place, it takes place in an 

 orderly and regular fashion, with the least possible injury 

 to the interests of the entire tree. From the very begin- 

 ning there has been arranged at the joint where the leaf- 

 stalk joins the stem, or where the separate leallets join the 

 central mid-rib, a row or articulation composed of cellular 

 tissue, and specially designed to act as a joint for the dry 

 leaves. When winter approaches, and chilly northern 

 storms are likely to tear to pieces the leaves on the trees, 

 all th(i protoplasm and other valuable cell-contents are 

 withdrawn into the permanent tissues of the plant, leaving 

 only the minor red and yellow colouring matters — mostly 

 effete and used up foodstuffs — which give so much beauty 

 and glory to the general aspect of our autumn woodlands. 



Then the articulation dries up and withers, and the dead 

 leaf separates at the joint, leaving behind it a regular mark 

 or scar, which is the visible token of Nature's definite 

 precaution against the northern cold and tempests. 



It was not always so, however, and it is not so esen now 

 in the greater part of the modem world that we ourselves 

 inhabit. It seems quite natural to us northerners that 

 " leaves have their time to fall " ; so natural, indeed, that 

 we almost forget the strict limitation of the practice to our 

 own chillier latitudes. Yet in reality the existence of 

 deciduous trees is a mere temporary accident of the here 

 and the now, a passing consequence of the great cold spell 

 which had its culminating point in the last glacial epoch, 

 and from whose lasting efl'ects we ourselves are even still 

 apparently suffering. Whether, as Mr. Alfred Russell 

 Wallace seems hopeful enough to believe, our poor old 

 planet may yet recover from this premonitory chilling or 

 not — whether we may yet look forward to a few more warm 

 spells or otherwise, before the final numbness of all dying 

 worlds comes upon us, is a question rather for the con- 

 sideration of astronomers and physicists than of the mere 

 mundane-roving naturalist, with his petty ephemeral 

 interests in our own plants and animals ; but one thing 

 at least is certain, that till a very recent period, geo- 

 logically speaking, our earth enjoyed a warm and genial 

 climate up to the actual poles themselves, and that all its 

 vegetation was everywhere evergreen, of much the same 

 type as that which now prevails in the modern tropics. 

 Indeed, we have only to look at the existing state of things 

 in order to see how very slight is the effect that has thus 

 been produced upon our temperate flora. For example, 

 among the oaks alone, there are some twenty species in 

 Europe, of which southern Europe has eighteen, mostly 

 evergreen, while north of the Alps tVere are only two, or 

 at most three, all of them deciduous. From the evolu- 

 tionary point of view it is clear that the northern kinds 

 are modern developments, specialised to contend with the 

 peculiarly cold conditions of sub-arctic Europe. 



Fortunately, too, we are not left in this matter to mere 

 conjecture or analogy : thanks to the researches of Heer 

 and others, we have positive geological facts to guide us, 

 which show conclusively that up to the Miocene period, 

 Europe was covered by forests of large-leaved evergreen 

 trees, of what we should now consider distinctively tropical 

 types. Ever since the Miocene, and on to the culminating 

 point of the great Ice Age, the European climate has been 

 growing steadily colder, and the European flora has been 

 at the same time steadily adapting itself to the new con- 

 ditions, and to assuming what we now consider a typically 

 northern aspect. During all that time, the large-leaved 

 evergreens gave way before the deciduous trees and the 

 chillier conifers, beginning at the north pole, and spreading 

 gradually southward, as the cold deepened and widened its 

 range. Since the end of the great Ice Age, and the 

 subsequent slight amelioration of the climate in northern 

 Europe, a reverse process has begun to set in ; the arctic 

 types ha\e begun to recede slightly once more, and the 

 comparatively southern or t<'mperate types have pushed their 

 way nortliward to occupy the place from which they were 

 previously dispossessed by the newly-evolved kinds. It is 

 not necessary for us here to inquire into the causes of this 

 great cycle ; the facts are there, and for our present pur- 

 pose tliey are quite suflicient. They show conclusively, 

 when one follows them out in detail, that the evolution of 

 deciduous trees was concomitant with the growth of cold 

 conditions around the two poles : and that such trees now 

 exist only where winter extends for part of the year, render- 

 ing the evergreen condition an undesirable one. Even in 

 the tropics, indeed, we find on high mountains a belt o£ 



