56 



NATURE 



[May 



that it is unscienlific — unphilosophical — to state an hypothesis 

 or formulate a theory, and much more so to make a categorical 

 statement, when no antecedent facts are given nor any subsequent 

 verification attempted. Thus, Mr. Cockerell asks the question, 

 " Why is it that plants growing on exposed sea-shores have a 

 tendency to lie upon the ground or otherwise to evade the 

 violence of the winds" (my italics) ? Now, what evidence has he 

 to bring forward that the purpose of lying down is to evade the 

 violence of the winds? So far, it is nothing more than his 

 private opinion — an a priori assumption. It is true that he adds 

 a reason, but it is also drawn from his own consciousness, and 

 not from nature : " When a plant is growing among others, it 

 has to compete with them in raising itself into conspicuous- 

 ness." But do not dwarf plants ever compete ? My experience 

 of the South Downs, where plants are for the most part con- 

 siderably dwarfed, is that the struggle between them is a 

 severe one. Yet their flowers and foliage are fully exposed 

 to sunlight and insects, as well as to severe gales of wind. Mr. 

 Cockerell also appears to forget that what is true for one plant 

 is true for another, and each must try to overtop all the others. 



I would venture to warn our younger naturalists most ear- 

 nestly against this facilis descensus of a priori reasoning with- 

 out facts or verification. It has been the bane of metaphysics ; 

 and when a scientific man like Dr. Weismann puts forth, in 

 the name of science, most deplorable illustrations of it in his 

 late attempt to apply his theory to plants, it is time that some 

 one should venture to protest. 



In reply to his request, I would refer Mr. Cockerell to M. 

 Verlot's pamphlet " Sur la Production et la Fixation des 

 Varietes," in which he describes his method of creating and 

 fixing dwarf plants by sowing seed late in the season. Also to 

 M. Roujou's experiments in selecting the smallest seeds of 

 plants [yourn. d'Hist. Nat. de Bordeaux et du Sud- Quest, 

 1884). Mr. McNab also raised dwarf rhododendrons by using 

 pollen from the smallest stamens. Want of space forbids me 

 adding more on the subject. George Henslow. 



The Natural Selection of Indian Corn. 



In a former letter I had occasion to mention that Zea mdis 

 varies in its period of maturing, and that at certain altitudes 

 and latitudes, only some of the varieties {i.e. the early maturing) 

 are able to mature at all, the rest being absolutely eliminated by 

 natural selection in a single generation. A few days ago I 

 received, through the kindness of Mr. James Fletcher, the new 

 (1891) Report on Experimental Farms for 1890, published by the 

 Canadian Government, in which are numerous statistics of 

 experimental planting in different parts of the Dominion. On 

 p. 296, Mr. T. A. Sharpe gives an account of the result of plant- 

 ing twenty-nine different varieties of Indian corn at Agassiz, 

 British Columbia, which perhaps deserves notice, as illustrating 

 the above-mentioned facts in a particularly clear way. Of the 

 varieties planted (all exposed to the same kind of environment), 

 the majority did not form any ears at all. Some formed very 

 small ears, and others reached various stages of maturity, but 

 only a very few actually matured. 



For example, I will quote some of them : — 



No. I. Moore's Early Concord, corn matured, one of the 

 best. 



No. 3. Early Adams, corn matured to glazing stage. 



No. 6. Mitchell's Extra Early White Flint, produced some 

 matured ears. 



No. II. Marblehead Sugar, matured corn, ears very small. 



No. 12. Narraganset, sweet, corn did not fill to tips of cob. 



No. 14. Chester Co. Mammoth, no corn formed. 



No. 21. Golden Dent, no ears formed. 



T. D. A. Cockerell. 



3 Fairfax Road, Bedford Park, Chiswick, W., May 10. 



The Soaring of Birds. 



It seems a great pity that the simpler form of this question — 

 wherein birds soaring steadily rise, in a gentle breeze, over a 

 large plain— is needlessly complicated by the flight of sea-birds 

 over waves. 



We shall get the solution best by taking the former and less 

 complicated case, wherein the pelicans, adjutants, cyrus, vul- 

 tures, &c., slowly rise, by soaring alone, to great heights, under 

 conditions where up-rushes of air are quite out of the question. 



NO. I 125, VOL. 44] 



Upper Asam is a dead level, some 60 miles wide by 200 

 long, and over this area, wherein these birds rise by soaring 

 alone, the air-drift is almost invariably from north-north-east, 

 or else south-west, and at about 5 to 10 miles an hour. They do 

 not seem to rise in a dead calm, nor yet in stormy weather, and 

 I take it the desideratum is a slow air-drift, or gentle iteady 

 breeze. 



That there are no up-rushes of air, I have fairly good proof ii> 

 the small tufts of cotton, from the Bombyx malabaricum, which 

 cross the field of my telescope when examining the Noga Hills 

 at 10 to 20 or 30 miles ; these are always beautifully horizontal 

 at elevations from 200 to 2000 feet, coming from the plains and 

 hills north-east of us. 



So that out here there is no complication of the case by ver- 

 tical movements of the air, as at sea. The question is not how 

 large birds sustain themselves (without flapping their wings) in 

 a wind, when there are rising and falling and strata of "different 

 velocities " ; but how large birds like the cyrus, adjutant, peli- 

 can, and vulture can rise from 300 to 3000 feet, in a steady 

 breeze, without flapping their wings. 



It is not mere flotation ; they have to raise 20 or 30 pounds 

 some 2000 feet, in addition to what the albatross does. 



Surely this is the major question, at once simpler to see, and 

 more difficult to answer. 



In Nature (vol. xxiii. p. 10) I drew attention to this, and 

 sent a small diagram, to show how I thought it was done. I 

 have frequently observed the phenomena since, and see no 

 reason to modify my views. 



Firstly, these large birds do not soar in a dead calm, or a 

 storm, or during high winds. They prefer a steady breeze. 



Secondly, they rise from the ground, by flapping the wings, 

 and continue this till they are 100 or 200 feet up, and then 

 begin to soar, in right or left hand spirals, 100 or 200 yards across. 

 At each lap they rise lo or 20 feet, and make as many yards 

 leeway, drifting slowly ivith the wind, and continue thus to rise 

 until out of sight above. 



With a good telescope a bird can be easily followed after a. 

 little practice, and the only motion which can be seen is slight 

 and occasional movement of the tail, in steering. 



The legs (of the waders) are extended at full length behind, 

 the neck thrown on the back, and beak projecting over the 



The tips of the primary wing- 



feathers are always well separated in different planes. 



■ '~ , and strongly curved up, thus. 



evidently under great strain. 



The lifting power is evidently applied to them mainly, and 

 the plane of the outspread wings is not horizontal, but forms 

 part of an obtuse, inverted cone, as though a little centrifugal 

 force was implicated. 



The speed of the bird is always greater than the breeze, and 

 the resistance is unequal on opposite sides of the loop of the 

 spiral ; least when it travels with the breeze, and greatest when 

 on the opposite half, meeting it. 



It seems to me the solution is that, when going with the wind, 

 the bird gathers momentum by going down a slight incline, and 

 when it turns and meets the breeze, this extra momentum is 

 used in lifting the bird and carrying it over a shorter course. 

 Thus it starts the next lap at a slightly higher level, but some 20 

 yards to leeward. Variation of the speed of the wind at different 

 levels is here quite out of the question ; the bird, too, keeps to 

 its steady spiral, and as steadily ascends at each lap. 



I feel sure that Prof. Tait, Sir W. Thomson, and Lord Ray- 

 leigh will find the case I state a more profitable one to study 

 than the erratic flight or floating of sea-birds. The telescope I use 

 to watch and follow these birds when soaring is a 3*5" O.G. 

 power 50, with long tripod legs, and on a mattrass below I find 

 no difficulty in keeping a bird in the field, if at icco feet up. 

 My own idea is that all these birds go up there to sleep or doze. 

 Sibsagar, Asam, March 30. S. E. Peal. 



