April lo, 1890] 



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community to tolerate the company of such, which might be 

 called social selection. 



It is often assumed by writers on evolution that permanent 

 differences in the methods in which a life-preserving function is 

 performed are necessarily useful differences. That this is not so 

 may be shown by an illustration drawn from the methods of 

 language. The general usefulness of language is most apparent, 

 and it is certain that some of the laws of linguistic development 

 are determined by a principle which may be called "the survival 

 of the fittest ; " but it is equally certain that all the divergences 

 which separate languages are not useful divergences. That one 

 race of men should count by tens and another by twenties is not 

 detennined by differences in the environments of the races, or by 

 any advantage derived from the difference in the methods. So 

 easy recognition of other members of the species is of the highest 

 importance for every species; but difference in "recognition 

 marks" in portions of a species separated in different districts of 

 the same environment is no advantage. Under the same condi- 

 tions, habits of feeding may become divergent ; but, since any 

 new habit that may be found advantageous in one district would 

 be of equal advantage in the other district, the divergence must 

 be attributed to some initial difference in the two portions of the 

 species. 



I have recently observed that, of two closely allied species of 

 flat-fish found on the coasts of Japan, one always has its eyes 

 on the right side, and the other always on the left. As either 

 arrangement would be equally useful in the environment of either 

 species, the divergence cannot be considered advantageous. 



Osaka, Japan. John T. Gulick. 



Self-Colonization of the Coco-nut Palm. 



The question whether the coco-nut palm is capable of 

 establishing itself on oceanic islands, or other shores for the 

 matter of that, from seed cast ashore, was long doubted ; and if 

 the recent evidence collected by Prof. Moseley, Mr. II. O. 

 Forbes, and Dr. Guppy, together with the general distribution of 

 the palm, be not sufficient to convince the most sceptical person 

 on this point, there is now absolutely incontrovertible evidence 

 that it is capable of doing so, even under apparently very 

 unfavourable conditions. 



In the current volume of Nai ure (p. 276) Captain Wharton 

 describes the newly-raised Falcon Island in the Pacific ; and in 

 the last part of the Proceedings of the Royal Geographical 

 Society, Air. J. J. Lister gives an account of the natu ral history of 

 the island. From this interesting contribution to the sources of 

 insular floras we learn that he found two young coco-nut palms, 

 not in a very flourishing condition, it is true ; but they were 

 there, and had evidently obtained a footing unaided by man. 

 There were also a grass, a leguminous plant, and a young 

 candle-nut (Aleurites), on this new volcanic island — a very 

 good start under the circumstances, and suggestive of what 

 might happen in the course of centuries. 



W. BOTTING HeMSI.EY. 



On Certain Devonian Plants from Scotland. 



I AM indebted to Mr. James Reid, of Allan House, Blair- 

 gowrie, Scotland, for the opportunity to examine a collection of 

 fossil plants obtained by him from the Old Red Sandstone of 

 Murthly and Blairgowrie in Perthshire, some of which have 

 been noticed by Dr. Geikie in his " Text-book of Geology." 



The collection is remarkable for the striking resemblance of 

 the matrix and the contained vegetable debris to those of the 

 lower part of the Gaspe sandstones of Logan, and the species of 

 plants are, so far as can be determined, the same.^ 



Psilophyton princeps largely predominates, as in Gaspe, and 

 is represented by a profusion of fragments of stems and branches, 

 and more rarely by specimens of the rhizoma and of the 

 sporocarps. F. robiistius is represented by fragments of stems, 

 but is less abundant, and Arthrostigma gracile by some portions 

 of stems. On the whole the assemblage is exactly those of the 

 sandstone beds of the lower division of the Gaspe sandstones. 

 There is nothing distinctively Upper Devonian in the collection. 



The collection also contains two slabs of dark-coloured 

 sandstone from Caithness, one of which contains what appears 

 to be a fern stipe similar to those of the genus Rhodea. Another 

 shows a remarkable plant having apparently a short stem giving 



' See p.apers by the author, Journal Geol. Society, London, 1859, and 

 I'rQceedings Geol. Society, Edinburgh, 1877. 



origin to a quantity of crowded leaves which are long, narrow, 

 and parallel-sided, and show only a very faint linear striation. 

 This plant is identical both in the form and arrangement of the 

 leaves with that found in the Devonian of Canada, and which I 

 have named Cordaites angttstifolia. I have, however, already 

 stated in my Reports on the Flora of the Erian of Canada 

 (Geological Survey of Canada, 1871 and 1882), that I do not 

 consider this plant as closely related to the true Cordaites, and 

 that I have not changed the generic name merely because I am 

 still in doubt as to the actual affinities of the plant. Mr. Reid's 

 specimens would rather tend to the belief that it was, as I have 

 already suggested in the reports above cited, a Zostera-like 

 plant growing in tufts at the bottom of water. 



Some of the sandstone slabs from Murthly contain specimens 

 of rounded olijects referable to Fachytheca (Hooker), a genus 

 of uncertain affinities but characteristic of .Silurian and Lower 

 Devonian beds on both sides of the Atlantic. One of these is 

 perfectly spherical with a shining surface, and 275 mm. in dia- 

 meter, the others have been broken so as to show a central 

 cavity or nucleus about I mm. in diameter, and with a thick 

 carbonaceous wall partly pyritised and showing obscure radiating 

 fibres. Prof. Penhallow, of McGill University, has kindly ex- 

 amined these, and has compared them with slices of Pachytheca 

 from the Wenlock limestone, kindly communicated by Mr. 

 Barber, of Cambridge, and with specimens presented by Prof. 

 Hicks from the Silurian of Corwen and with specimens in the 

 author's collection from the Silurian of Cape Bon Ami ; and 

 also with the excellent figures in Mr. Barber's paper in the 

 Annals of Botany. He has not been able, however, to arrive at 

 any conclusions beyond the probable general similarity in struc- 

 ture of the various forms, which may, however, as Mr. Barber 

 suggests, have differed in their naUue and origin. The only 

 thing certain at present seems to be that these puzzling 

 organisms had a thicker outer coat of radiating fibres, and of so 

 great density that it was less liable to compression than the 

 other vegetable tissues with which it is associated. 



A few small specimens sent more recently by Mr. Reid con- 

 tain some curious but not very intelligible objects from the same 

 beds. One is a stem coiled at the end very closely in a circinate 

 manner. In form it resembles the circinate vernation of 

 Psilophyton princeps, but is much larger. It may belong to /'. 

 robtistins, or possibly to a fern, but is too obscure for certain 

 determination. Several others appear to represent flattened 

 fruits or sporangia of obovate form and of large size. One has 

 a stalk attached with what seems a rudiment of a bract, and 

 another shows obscure indications of having contained round or 

 disk-shaped bodies about 2 mm. in diameter. All show minute 

 longitudinal striation. I have not previously met with bodies of 

 this kind in the Devonian, and can only suggest that they may 

 represent the fructification of some unknown plant, possibly that 

 to which Pachytheca belonged. J. W.M. Dawson. 



Montreal, March 5. 



Exact Thermometry. 



I AM glad to observe that Prof. Sydney Young and myself 

 are now in substantial agreement as regards the tension theory 

 of the ascent of the zero in thermometers, and approximately 

 in agreement as regards the actual cause of the- ascent in the 

 neighbourhood of the ordinary temperature. 



Some time ago, in connection w ith an investigation of melting- 

 point, I devoted three years to an examination of the properties 

 of the mercurial thermometer. Among other conclusions which 

 then seemed to me probable, the application of the known 

 plasticity of glass under pressure to account for the enormous 

 ascent (in lead-glass) of the zero at high temperatures 

 appeared of some value. I have never advanced it as a mature 

 theory, and am perfectly open to correction on the subject ; but 

 neither Prof. Crafts (with whom I at that time discussed the 

 matter), nor any subsequent experimenter, has submitted the 

 suggestion to a crucial examination. 



Prof. Young's experiments (Nature, March 27, p. 489) are very 

 interesting as far as they go ; but the kind of glass of which his 

 thermometers are constructed is not that which brings out the 

 peculiarities of the material in their most striking develop- 

 ment. This, indeed, has long been known. It may well be that, 

 in German soda-glass, the plasticity is masked by a preponderat- 

 ing tendency of the harder or more crystalline silicates of the 

 bulb to set. Much could be done towards settling the question 

 as to plasticity, if three thermometers of lead-glass — one vacuous, 



