562 



NATURE 



[January 21, 1915 



the inlet of the condensation water was placed is not 

 stated in the report, but from the size of the vessel 

 it could not be very deep, and the best results could 

 scarcely be expected from it, and for the same reason 

 it would be of no use save in fine weather, owing to 

 the rolling of the vessel constantly changing the level 

 from which the water was drawn. Still, under calm 

 conditions, it might have been deep enough to touch 

 in some cases Prof. Barnes's rising temperature. 



Prof. Barnes's results are so consistent and definite 

 that they carry conviction, and one can scarcely imagine 

 that the observations taken when sailing towards, 

 and from, an iceberg in many different directions, 

 which enabled him to draw the isotherms all round the 

 berg as given in his report and reproduced in your 

 issue of December 12, 1912, could be the result of 

 chance, and not of something which had a real 

 physical existence. It is possible that the conditions 

 there represented may be rare, as they seem to indi- 

 cate that the berg and the water had travelled together 

 for a long time. It seems probable that in many cases 

 the distribution of the isotherms will not be so regular 

 owing to the berg and the water moving at different 

 rates and in different directions. One conclusion we 

 may, however, come to from the Scotia's observations 

 which is that the explanation of the rising tempera- 

 ture on approaching Icebergs is nol due to radiation 

 as supposed, as the registering thermometer on the 

 Scotia, though not as sensitive as that used by 

 Prof. Barnes, was yet easily capable of detecting 

 changes such as those indicated by Prof. Barnes's 

 thermograms. It is to be hoped that the subject 

 will be further Investigated after the war Is ended. 



John Aitken. 



Ardenlea, Falkirk, January 4. 



The Longevity of Seeds. 



In the note In Nature of January 7 (p. 515) upon 

 Mr. Shull's paper in the Plant World, referring to the 

 longevity of seeds, it is stated that this " is a subject 

 on which specific information Is always desirable." 

 The following, therefore, may at least contribute sug- 

 gestion. 



In 1862, my father, at a cost of 4000L, caused 

 Dowalton Loch, the largest sheet of water In Wig- 

 townshire, to be drained. The operation attracted 

 considerable attention at the time, owing to the subse- 

 quent exploration of a number of "crannogs," or lake 

 dwellings of the fascine type which were laid bare. 

 The bottom of the lake, about 200 acres In extent, 

 was for the most part covered with deep mud and 

 peat ; but across the centre of it lay a ridge of broken 

 rock, now a dense jungle of dog willow (Salix caprea), 

 whereof the seeds were no doubt wind blown. 



Six years ago I was clambering among these rocks, 

 and, coming upon an open space in the thicket, found 

 to my surprise that the ground, to the extent of nearly 

 an acre, was thickly covered among the stones with 

 a carpet of Pyrola minor. Nowhere, except in Nor- 

 way, have I seen this pretty plant In such profusion. 



Now, although I have given fairly close scrutiny 

 to the phanerogamous flora of this country, I have not 

 found P. minor within its bounds, though for fort}- 

 years I have known of a colony of it In the neigh- 

 bouring county of Kirkcudbright, about five and 

 twenty miles in a straight line from Dowalton Loch. 

 P. rotundifolia also grows on the banks of the Cree 

 about twenty miles distant. 



No doubt P. m,inor once abounded In Wigtownshire, 

 but It has disappeared under the plough, though it 

 may linger still in the remote moorland. Dowalton 

 Loch lies in the heart of an arable, closely cultivated 

 district. Whence, then, did the minute seeds come 



NO. 2360, VOL. 94] 



which have produced this surprising crop ? Have they 

 lain dormant under the waters of the loch since the 

 days of the lake-dwellers, or — a more moderate guess 

 — since the days when the primeval forest bordering 

 the lake was cleared away and the land broken up for 

 tillage? 



I shall be happy to receive a visit from anyone who 

 may desire to verify for himself the topography of 

 the district in connection with this Isolated mass of 

 Pyrola. Herbert Maxwell. 



Monrelth, January 11. 



S. T. Coleridge and the Immortality of the Protozoa. 



That Welsmann's aphorism regarding the '•im- 

 mortality " of the Protozoa had been uttered by others 

 before him is not unknown ; and Mr. Clifford Dobell 

 in a recent paper ascribes to Ehrenberg the first 

 expression of the Idea. Ehrenberg 's book was pub- 

 lished In 1838 ; but Coleridge had said the same thing 

 many years before in his " Blographia LIterarIa," 

 published in 1817 and written a couple of years earlier. 

 In a footnote to chap. iv. (on Wordsworth's " Lyrical 

 Ballads") he says: "There is a sort of minim im- 

 mortal among the animalcula infusoria, which has not 

 naturally either birth or death, absolute beginning 

 or absolute end : for at a certain period a small point 

 appears on its back, which deepens and lengthens 

 till the creature divides into two, and the same pro- 

 cess re-commences In each of the halves now become 

 integral." No statement of the case could well be 

 plainer or more precise than this. I wonder whether 

 Coleridge was indeed the first to make It ; or whether 

 some one of the eighteenth-century naturalists had 

 already drawn the Inference — not, after all, a very 

 profound one — that a creature which multiplies by 

 simple fission " has not naturally either birth or 

 death," and may be called "immortal." 



D'Arcy W. Thompson. 



The Cause of Streaks upon Lath-and-Plaster Walls. 



For some time past I have been observing the 

 streaks which occur upon lath-and-plaster walls. I 

 have made a survey of the literature and find no 

 adequate treatment of the phenomenon. For that 

 reason I take the liberty of submitting to you the 

 results of my observations In the hope that you may 

 find them worthy of publication. The results of my 

 observations are as follows : — 



(i) The striatlons are accumulations of dust upon 

 the surface of the plaster. They may be wiped off 

 with a cloth. 



(2) The phenomenon occurs only on warmer sur- 

 faces of walls which are exposed on the other side 

 to out-of-doors or to colder rooms. 



(3) The steeper the temperature gradient through 

 the wall, the more pronounced is the phenomenon. 



(4) The light streaks, the spaces comparatively fre? 

 from dust, occur over laths and joists, the dark streak^ 

 over the spaces between them. 



Poynting and Thomson ("Text-book of Physics 

 Heat," p. 152) suggest "that the phenomenon Is 

 probable illustration of 'radiometer action.'" TM 

 areas of plaster backed up by wood are probablj 

 warmer than those areas not so protected. From the 

 supposedly warmer area an approaching dust particle 

 is repelled by a more vigorous molecular bombardment 

 than it encounters upon approaching the supposedly 

 colder area. 



I was led to inquire whether this explanation is a 

 complete one upon observing what appears to be a 

 related phenomenon. In a room rather free from dust 

 but quite damp, the areas of plaster which ordinarily 

 would be streaked with dust were quite clean, but 

 were much discoloured by water. This observation f 



