Oct. 31, 1884.] 



♦ KNOV/LEDGE ♦ 



'363 



>N ILLUSTRATED 'SJltr' MJ. 



MAGAZINE OF SCIENCE 



LONDON: FRIDAY, OCT. 31, 1884. 



Contents op No. 157. 



PA6B 



Ivy. By Grant Allen 353 



Our Two Brains. By R. A. Pro<!tor 354 

 The Workshop at Home. {Illus.) 



By a Working Man 356 



Dickens's Story left Half Told. By 



Thomas Fl>ster 356 



Dreams. XI. By E. Clodd 368 



Tricyclf Exhibitions 359 



The Earth's Shape and Motions, 



By R. A. Proctor 359 



Match-Lore 360 



Rambles with a Hammer. By 



W. Jerome Harrison, IT.O.S 361 



PAGB 

 International Health Exhibition. 



XXII. The Present Aspect of the 



Sewage Question 363 



The Society for Psychical Research. 



{llhia.) 361 



British Seaside Resorts. By Percy 



Russell 366 



Reviews 368 



Miscellanea 369 



The Inventors' Column 370 



Correspondence ; The Truth about 



Koch's Cholera Germ, &c 371 



Our Chess Coloma 374 



IVY. 



By Grant Allen. 



THOUGH every one of us has been perfectly familiar 

 with common ivy from his boyhood, upward, I wonder 

 how many jieople have ever noticed its pretty bunches of 

 thickly-clustered, pale yellowish-green flowers that form 

 such large and prominent masses in the early autumn. 

 They are just now in full blossom, and are attracting, as 

 usual, the flies and bees in great numbers to their abundant 

 store of easily-accessible honey. Let us stop for a while 

 beside some knotted stem that clambers close against some 

 low wall, and examine this old, familiar favourite in the 

 new light cast upon it by the discoveries of modern bio- 

 logical science. 



Ivy is a native English evergreen creeper, one of the 

 very few large-leaved evergreens really indigenous to our 

 islands ; for though the laurels, and aucubas, aud laurus- 

 tinuses, and rhododendrons of our shrubberies have made 

 us now perfectly at home among the class by naturalisation, 

 yet almost all our true British evergreens are more or less 

 needle-leaved conifers, such as the Scotch fir, the yew-tree, 

 and the juniper. Holly, an undoubted native of England, 

 and box, which is very probably an introduced alien, are 

 its chief compeers in this respect. In its truly wild state, 

 the lower branches of ivy creep along the soil, while 

 the main stems climb up trees, walls, or rocks, to 

 which they adhere by means of small fibrous root- 

 like excrescences. This is one out of the many 

 ways adopted by comparatively feeble plants to raise 

 themselves, half parasitically (so far as support alone is 

 concerned, I mean) up the stout trunks of other and more 

 sturdy woodland competitors. Compare it, in this respect, 

 with the straggling arched-branches of the common black- 

 berry bramble, loosely festooned by means of their curved 

 and hooked prickles over the blackthorns and May-bushes 

 in the wastes and hedges ; or with the little sucker-like 

 supports of the Virginia ci'eeper, clinging fast to the tiny 

 crannies and asperities of a brick wall here in England, as 

 it clings in its native woodlands to the chinks and rugosi- 

 ties in the bark of trees ; or with the twining tendrils of the 

 pea, really abortive leaflets, that twist twice or thrice or even 



oftener round the twigs and branchlets of the supporting 

 bushes; or with the curling leaf-stalks of the canary creeper, 

 where the petiole of a true and active leaf performs the same 

 clasping function. In every case, the end to be attained is 

 the same — the plant endeavours to raise itself by means of 

 some tree, shrub, or bush, above the competing mass of 

 foliage on the ground below, and to reach the open air and 

 free sunlight overhead ; but by what an immense variety 

 of means it attains in various cases this desired result ! 

 Ally trick of habit, be it hooked hair (as in goosf grass), 

 or twining stems (as in convoh-ulus), or mouth-like suckers 

 (as in dodder), or twisted leaf-stalk (as in clematis), that 

 happens to aid in this object, is immediately seized upon 

 by natural selection, and developed and encouiaged into an 

 organic peculiarity of the whole species. In our little 

 English flora alune, to go no further, it ia an interesting 

 study to look at all the cases above enumerated, side by 

 side with those of bryony, tamus, wild madder, dog-rose, 

 cinquefoil, vetches, hop, and periwinkle, whose diverse 

 modes of obtaining this single end should be noticed in 

 detail by the country walker. 



The leaves of ivy form by far the most conspicuous part 

 of the plant to most ordinary outside observers. Their 

 shape is very characteristic, so much so that the epithet 

 " ivy -leaved " has been given to many other plants, such as 

 the ivy-leaved ranunculus, the ivy-leaved veronica, and the 

 ivy-leaved toadflax. It is a noteworthy fact, too, that all 

 the plants possessing foliage of this peculiar broadly-lobed 

 form are trailers or climbers ; and in most of them the 

 leaves habitually form a single layer — lie one deep only — 

 over the wall, or tree-trunk, or soil on which the plant is 

 creeping. In short, this form of leaf seems specially 

 adapted for climbing plants ; its angles dovetail neatly 

 into one another, and the tip of each tills the hollow at the 

 stalk of its neighbour, so that every leaf obtains the full benefit 

 of the sunlight on all its parts, without interfering with the 

 equal illumination of its like-minded fellows. I do not say 

 that this is the only, or even the best, way for obtaining 

 that result; but it is one way, and a suflicient way; and 

 that is all that natural selection can, as a rule, succeed in 

 securing. One has only to look at a mass of wild ivy 

 creeping up a wall or tree in order to see how admirably 

 the whole body drapes the entire space it covers, leaving 

 very few interstice.^, yet seldom casting a shadow over any 

 part of its own surface. I say " wild ivy," because many 

 of the cultivated exotic varieties in our gardens, being 

 grown for the sake of their luxuriant leafage alone, under 

 artificial conditions, in richly-manured soil, produce copious, 

 masses of over-lapping leaves very diflerent from the native 

 parsimony of the indigenous field species. 



Observe, however, that the leaves upon the upper flower- 

 ing branches are extremely unlike in form to those which 

 cover the naked wall with their bright verdure. These 

 upper shoots rise freely into the air, and have rounded or 

 oval leaves, not at all "ivy-shaped," disposed pretty equally 

 on every side, so as to catch the open sunlight into which. 

 they have raised themselves. The upper leaves often some- 

 what resemble lime leaves or laurustinus-leaves in general 

 outline ; and they clearly show how much the shape of the 

 foliage depends upon the surrounding conditions of air and 

 sunshine. Where these conditions of growth are supplied 

 one-sidedly, as on the wall, the foliage is all turned out- 

 ward, and so shaped as to economise every portion ; where 

 they are equally diS'used all round, the foliage grows out 

 alike on every side, and avoids mutual interference by its 

 spiral arrangement along the central axis. Very starved 

 ivy, on a dry wall, has usually very reduced and deeply- 

 divided leaves, with finger-like lobes ; very luxuriant ivy, 

 when it oveitojis its support, ha? usually very full and 



