374 



NATURE 



\March i, 1877 



of carbonic acid. It is accompanied by a molecular 

 change which renders the resulting product soluble and 

 diffusible. Assimilation is simply the absorption by the 

 living tissue of the substances thus prepared, one of the 

 chief processes which accompanies it being the rever- 

 sion, by loss of water, of the glucose to the condition of 

 cellulose, a substance isomeric but not isomorphic with 

 starch. Intussusception, therefore, is a process which 

 can only succeed digestion. No essential difference can, 

 in fact, be maintained between the manner in which 

 animals and plants digest their food, A. W. B. 



LETTERS TO THE EDITOR 



[The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications^ 



Hygroscopic Seeds 



I HAVE lately received an interesting letter from Fritz M tiller, 

 in St. Calherina, Brazil, on the subject of hygroscopic seeds. He 

 tells me that in the highlands of the Uruguay he has succeeded in 

 discovering more than a dozen grasses, as well as a species of 

 geranium, whose awns are capable of hygroscopic torsion. He 

 has been so kind as to send me specimens of the grass-seeds, 

 and many of them appear to be as beautifully adapted as those 

 of Siipa, Avena, &c., for penetrating the ground in the manner 

 which I have elsewhere described.^ The mot curious among 

 the specimens received are the seeds belonging to the genus Aris- 

 tida. In one of these the awn is longitudinally divided into 

 three fine tails, six or eight inches in length, each of which twists 

 on its own axis when the seed is dried. These tails project in three 

 directions, and more or less at right angles to the axis of the seed, 

 and Fritz Miiller states that they serve to hold it in an upright 

 position with its lower end resting on the ground. The seed is 

 pointed and barbed in the usual manner, and when it is made to 

 rotate by the twisting of the awns, it evidently forms a most 

 effectual boring-irstrument, for Frilz Miiller found many seeds 

 which had penetrated the hard soil in which the parent plant 

 was growing. Another species of Aristida is interesting to me, 

 because it illustrates the explanation which I gave of the torsion 

 of the awn of Stipa, namely, that each individual cell of which 

 the awn is composed is capable of torsion, and their combined 

 action results in the twisting of the whole awn. Now in this 

 species of Aristida, each of the three tails into which the awn is 

 divided is capable of torsion on its own axis, and as the seed dries 

 they twist up into a perfect three-stranded rope, just as the com- 

 ponent cells combine to produce the rope-like twist of the Stipa 

 awn. And as the tails wind together and form the strands, the 

 seed is made to rotate and thus bury itself in the ground, 

 Down, Beckenham, February 19 Francis Darwin 



Mind and Matter 



But for illness I would have made an earlier reply to 

 Mr. Duncan's courteously-expressed objections (Nature, vol. 

 XV., p. 295) to my analysis (Nature, vol. xv., p. 217) 

 of his very ingenious "solution" (Nature, vol. xv., p. 

 78). A general "mistake," and an " essential omission," are 

 the charges against me. The mistake is in " regarding what 

 was intended to solve a problem as intended to prove an alleged 

 fact." "The alleged fact," he adds, "that consciousness 

 depends on nervous organisation, I assumed to be a fact, and 

 undertook to indicate hoiu the dependence might be conceived, 

 or regarded, to exist." He says that I clearly understood this 

 "at starting." Where now is it that I " fell into the error?" 

 His first step towards " clearing away difficulties in the way of 

 our conceiving the relation of consciousness to matter," is to 

 allege this fact : " It is no more difficult to conceive of matter 

 being subjective than of spirit being subjective." This is a 

 dogmatic staterrient about our powers of conceiving ; no hint of 

 help as to how we may conceive. We ordinarily conceive of 

 "spirit" — the "ego," the "subject" — as susceptible toconscious- 

 ness, or "subjective," because we (the ego) feel we are conscious; 

 but is it " as easy " to conceive of a stone as susceptible to con- 

 sciousness, i.e. subjective? To say it is, I called 2t.petilio prin- 



' Trans, Linn. Soc, vol. i., part 3, p. 149, 1876. 



cipii, because it assumes that conceivability which has to be 

 estabhshed. I used the word " probability " as involving con- 

 ceivability ; for can we intelligibly assume a probability without 

 a conception of what that proba'nili-y is? But Mr. Duncan 

 contends that his position is " conceivable as a hypothesis, true 

 or false." Unquestionably we may conceive some one stating 

 any hypothesis— a stone feels, fire freezes— but to conceive one 

 doing this is not to have a concept of any part of the operation 

 as hypothesised, however we may attach a meaning to the terms 

 as such. Again, if any hypothesis, true or false, is already con- 

 ceivable, this fact cannot favour Mr. Duncan. 



So far I have not been led "to mistake allegations of the 

 conceivability of a notion for assumptions or intended proofs 

 that the notion is true." To the next position, " How energy is 

 related to matter, is no less mysterious than how subjectivity 

 may be a property of matter," my objection was twofold : first, 

 to the illogical form ; second, to the argument itself. Mr. Duncan 

 replies, " The parity of mystery was not intended to establish parity 

 of probability as to facts, but merely parity of conceivability." 

 Now what is conceivable in the known case? Theya<r/of energy 

 being related to matter. Next, whit here is mysterious or incon- 

 ceivable? — the manner how these are related. Finally, what is the 

 parallel to establish ? Mr. Duncan answers, " Not the parity of 

 probability as to facts, but merely parity of conceivability." 

 But the conceivability of hoiu energy is related to matter equals 

 zero, therefore, by parity of reasoning, the conceivability of how 

 subjectivity is related to matter equals zero. I commented, 

 therefore, on all that this argument supplied — a bare shadow of 

 probability. My next objection to the position, "Energy may 

 be divided, why not subjectivity ?" is strictly categorical, and no 

 flaw has been found in it, nor, intrinsically, in any of my objec- 

 tions, which have now been shown to apply to " conceivability." 

 Of the omission, Mr. Duncan says : — "The essential part of my 

 solution which indicated roughly the modus of the connection 

 between matter and consciousness, and which dealt with the 

 great difficulty of the question. How to account for the two 

 aspects of matter, the conscious and the unconscious ? has not 

 been touched by Mr. Tupper." Because all this was based on 

 the untenable ground that "subjectivity may be divided," I 

 closed my analysis here ; but will conclude with a few remarks , 

 on the ingenious and original parallels drawn by Mr. Duncan. | 



"As energy potential is rest, so subjectivity potential is un- 

 consciousness. As kinetic energy is motion, so active subjectivity j 

 is consciousness." Now energy, both to the materialist and his 

 opponent, is a hypothesis, not a phenomenon ; and it is not 

 legitimate to support one hypothesis by another. 



Again, if subjectivity is defined " susceptibihty to conscious- 

 ness," some sub-definition of " susceptibility " is neeo'cd ; for if 

 non-innervated matter, as Mr. Duncan admits, is never conscious, 

 then matter in this form being non-susceptible to consdousness, is 

 by the definition non-subjective : a conclusion opposed to Mr. 

 Duncan's " all matter is subjective or susceptible to conscious- 

 ness," his qualification, that non-innervated mat'.er is only 

 "potentially subjective" not availing unless this term mean 

 non-subjective, and leave us with the above contrad'Ction. The 

 expression " all forms of matter may, by innervation, be made < 

 susceptible," &c., would indeed carry the conclusicn "all matters 

 maybe made subjective," but then subjectivity would be an i 

 accident, not a property of matter as defined b' Mr. Duncan. 

 Lastly, to the phenomenalist who would investigate, and not 

 create, nature, matter, or a fancied common svbstance for the 

 support of all phenomena, is perhaps ,the most unwarranted of 

 all assumptions. /. L, Tupper 



Atmospheric Currents 



Mr. Clement Ley thinks (see his letter in Bature, vol. xv 

 p. 333) that if the earth's atmosphere con&ined no wateiy 

 vapour, the great currents of atmospheric ciculation would be 

 quite unlike what they are. I think, on the contrary, it is as 

 certain as the established truths of physical astronomy, that il «1 

 there were no watery vapour the great curreiis, though not the | 

 storms and other temporary disturbances, woud be nearly what f 

 they actually are. 



All winds belonging to the great currents though not loca I 

 winds, form part of a system of circulation between the eqna | 

 torial and the polar regions, which is caused by the difference 

 those regions in temperature. Equatorial airis constantly flowinn 

 towards the poles, and polar air towards tht equator ; the equal 

 torial air brings the greater rotatory velocit/ of the equatorial 



