NA TURE 



[February 24, 1910 



Among moulds, certain species of Mucor exist as several 

 races the individuals of each of which reproduce them- 

 selves asexually, but do not conjugate with one another. 

 When, however, individuals of different races meet, they 

 conjugate and produce zygospores. It may be supposed 

 that one race is of such a type as MM_^, another of the 

 tnmFF type. In this case verification of the hypothesis 

 is possible. 



The absence of sexual reproduction in various groups of 

 fungi is to be explained on the present hypothesis as due 

 to the extinction (or effective separation) of all zygotes 

 except those of one type, e.g. the M/ or the mF types. 



In homosporous ferns, the spores, produced after the 

 reduction division, give rise each to a prothallus which 

 bears male and female organs. If it be allowed that the 

 reduction division is of fundamental significance with 

 respect to the segregation of characters, it would appear 

 to follow that current Mendelian theories of sex-heredity 

 fail to account for the fact that a spore produced as a 

 consequence of the reduction division may yet carry 

 " male " and " female " factors. 



The phenomena mav be interpreted simply in terms of 

 the new hypothesis. The fern plant is MMFF ; the spore, 

 and hence the prothallus, carries MF. Therefore male and 

 female organs may be produced by the prothallus. The 

 gametes formed and matured in the female organs are 

 " female," those formed and matured in the male organs 

 are " male." 



In the heterosporous ferns the spores are of two kinds, 

 macrospores, giving rise to " female " prothalli, and micro- 

 spores, which give rise to " male " prothalli. In terms of 

 our hypothesis the sporophyte (zygote) is MniF/, the mega- 

 spore mF, and the microspore M/. 



Further, the high rate of mortality which accompanies 

 spore-formation receives on this hypothesis an intelligible 

 explanation. It is due to the inevitable reappearance of 

 combinations of sex-characters which the heterosporous 

 fern has ceased to tolerate. 



In the light of the present hypothesis, homosporous 

 ferns are homosporous because they are homozygous, and 

 heterosporous ferns are heterosporous because they are 

 heterozygous for the sex characters M and F. 



The significant question arises, How far is the present 

 limitation of characters presented by any great group of 

 organisms determined by the fact that in this group the 

 task of reproduction has come to be committed to some 

 particular type or types of gametes? 



The hypothesis would appear to throw light on large 

 numbers of known facts, on prepotency, partial sterility — 

 such, for example, as occurs in heterostylism — the appar- 

 ently excessive production of pollen and ovules, and so 

 forth. 



Not only is it not repugnant to a reasonable explana- 

 tion of many facts, but also the hypothesis does not 

 seem to be inherently improbable. In that it is based 

 on the presence and absence theory, it receives the 

 sanction of Mendelism. It tempts the imagination to trace 

 the origin of sexuality from the " self-contained "organisms 

 of the MF type. Evolution in such types took, in some 

 individuals, the form of a dropping out of the M, in 

 others, of a dropping out of the F, factor. Such incomplete 

 forms as M/ and Fm discovered in fusion the means of 

 restoring their constitutions ; but out of this fusion possi- 

 bilities for novel constitutions arose, for the MmF/ type 

 of zygote was now in being. In reproducing by segregation 

 the original MF type of gamete, the zygote "vas constrained 

 to produce likewise the other possible combinations of 

 Mm and F/. Fusions between the several types resulted 

 in different forms of zygote; evolution had its chance. 



Among other types, the pure recessive, mmff, arose, and, 

 with its advent, sterility, and, it may be, death, came on 

 the scene as the sinister shadow of " sexual " reproduction. 



It only remains to add to this note that — in case the 

 hypothesis it proposes prove of value — though the responsi- 

 bility for the hypothesis rests with the writer, the stimulus 

 to which it owes its inception originated, in the first place, 

 from a study of Bateson's work on heredity, and in the 

 second place from discussions on the problems of heredity 

 between the writer and his colleagues. Miss Rayner, Mr. 

 Jones, and Miss Pellew, of the botanical laboratory, to 

 whom certain of the foregoing illustrations are due. 



University College, Reading. Frederick Keeble. 



NO. 2104, VOL. 82] 



Geology and the Earth's Axis of Rotation. 



Fro.m time to time the pages of Nature contain refer- 

 ences to the theory which would e.\plain the occurrence 

 of Ice ages by a hypothetical shifting of the earth's axis 

 of rotation. On the face of it, the theory in question 

 appears to be capable of explaining a good deal more 

 than this. 



In the first place, if the axis of rotation were to be 

 shifted, it seems clear that the relations between the 

 earth's hydrosphere (or hydrospheroid) and the lithosphere 

 must undergo change. In the regions towards which the 

 pole is approaching land will tend to emerge from the 

 sea, and vice versa. If the effects of this supposition be 

 traced out in detail, they will be found to furnish nn 

 explanation of such phenomena as raised beaches, sub- 

 merged river valleys, varying continental connections, 

 &c., without postulating violent alterations in the litho- 

 sphere itself. Speaking merely qualitatively, the hypothesis 

 seems to fit the facts pretty closely, e.g. (a) the height of 

 raised beaches tends to increase as one approaches the 

 polar regions, as it ought ; (fe) a marine transgression is 

 associated with a warm climate. 



In the second place, a shifting of the polar axis will 

 not be without effect on the lithosphere itself, although 

 such effect would not, presumably, under present con- 

 ditions, at all resemble the effect on the hydrosphere already 

 alluded to. Even in a rough qualitative way this effect 

 is not easily traced out, but it seems tolerably clear that 

 it will account for those processes of folding, &c., whereby 

 mountain chains are built up, and also for extensive local 

 subsidences such as are believed to have occurred in geo- 

 logical time. These, and doubtless other phenomena, the 

 hypothesis explains without having recourse to the sup- 

 position that the earth has been undergoing contraction 

 through loss of heat. 



I am not aware of the existence of any publications 

 dealing with the matters referred to, but as the subject 

 appears to be not without interest, perhaps some of your 

 other readers will be able to refer me to papers, &c.. 

 treating of the subiect with which they may he 

 acquainted. I should be particularly glad to be referred 

 to researches in which the subject is treated quantitatively. 



Hugh Birrell. 



Holyrood House, Bo'ness, Linlithgowshire, N.B., 

 February 4. 



Secondary Cells in Tropical Climates. 



.•\ll who have used batteries of small secondary cells in 

 the tropics will have experienced the difficulty of keeping 

 their cells in efficient working order, and especially in 

 preserving the junction of separate cells from rapid 

 corrosion. The difficulty, appreciable in Europe, becomes 

 very serious in .1 climate where the laboratory temperature 

 lies between 30° and 40° C, and for this reason — it is 

 probable that practically all accumulators sent to tropical 

 countries by European manufacturers are filled by their 

 recipients with dilute sulphuric acid of a density (1,190) 

 which corresponds to a 20 per cent, mixture in north 

 Europe at 15° to 20° C, but at a temperature of 

 30° to 35° C. indicates a mixture which is far too rich in 

 acid for the health of the cells. Some simple experiments 

 recently carried out in this laboratory exhibit quite clearly 

 how large a deviation from the standard 20 per cent, 

 mixture is caused by filling cells at 30° with dilute asid 

 of density t,iqo. It is found that a density of i.iQO at 

 30° corresponds to a composition of 23 per cent., whereas 

 the value of the composition accepted as givinc the best 

 results with cells of this type is 20 per cent. The differ- 

 ence is as much as half the total change in composition 

 due to chemical action during the process of charging the 

 cell. 



The conclusion reached from an examination of the 

 density-temperature curves for dilute sulphuric acid points 

 to the advisability of filling all secondary cells in localities 

 where the average temnerature is -^0° or more with acid 

 solution of density about 1.T70. Densities as low even as 

 1,150 have been found satisfactory for small secondary cells 

 in the hot weather in Calcutta. 



In the case of Large plants in power stations, the matter 

 may be still more important, as a cell containing too strong 



