yttne 23, 1881] 



NATURE 



169 



did raise the temperature of the calorimeter. I liave tried to 

 repeal this experiment, but I never could obtain the whole bulb 

 of the thermometer entirely covered with sheets of sublimated 

 ice, and without this the experiment will be illusory. Many times 

 I obtained lozenges of sublimated ice, which did adhere very 

 strongly to the bulb of the thermometer, until it show ed + 35° 

 or + 40° C. Then the lozenijes generally fell off. 1 do not 

 consider this to be any deci'ling proof, as it may depend on a 

 phenomenon similar to that of Leidenfrost, nor do I think it very 

 probable that ice really can exist at those temperatures, but if 

 that should be the case the simplest manner to account theoreti- 

 cally for the exi-tence of hot ice would be to assume a new allo- 

 tropic modification, since it may be regarded as a matter of fact 

 that ordinary ice cannot be heated over the limits pointed out by 

 Regnault. If this should be the case I think that the i;nportancc 

 of the discovery of Dr. Carnelley could hardly be overrated. 

 Upsala, May 28 Otto Pettersson 



Temperatitre of Rain-water. — "A Subscriber" asks 

 where he can find records of the temperatures of rain-water 

 when falling, and of the earth a few inches bel )w the surface, 

 during any or all the months of the year. — As regards the 

 British Islands, the most extensive and long-continuel observa- 

 tions on the temperature of the soil are those published by the 

 Scottish Meteorological Society since 1857. A resume of the 

 first five years' observations was published in the Society's Qutr- 

 terly Repert for Oct )ber-December, 1S62. In the Society's 

 younial (vol. i. p. 320) is a di-cu^sion of valuable series of 

 observjtio is made on the temperature of drained aid undrained 

 land at various depths ; also in Journal (vol. ii. p. 273, and 

 vol. iii. p. 211) discussions of hourly observations on the tem- 

 perature of the soil and of the air at different stations in Scot- 

 land. With respect to the temperature of falling rain, little, if 

 anything at all, quite satisfactoiy, has been accompli hed, the 

 practical difficulties in the way being either not apprehended by 

 the ob-erver or not satisfactorily disposed of Our c irre^p mdent 

 may also consult with advantage the publications of the various 

 Continental organisations for the pr^jsecution of forest meteor- 

 ology. — Ed. 



NOTES ON ALG^' 



THE publication of the second part of Bornet and 

 Thuret's volume on Algs seems a fitting opportunity 

 to notice it in some little detail. While the First Part, 

 published in 1876, treated chiefly of the red Alga:, by far 

 the larger portion of this Part treats of the Nostocs ; 

 while the First Part contained a good deal of the notes of 

 Thuret, the present is practically the work of Bornet, and 

 the drawings are in almost every instance from this 

 author's pencil. 



Under the modest title of Notes, we find in this hand- 

 some quarto volume, of over a hundred pages and twenty- 

 four plates, in addition to notes on the higher Algs, a 

 most exhaustive treatise of a very interesting group of 

 simple Phycochromaceous plants. 



The illustrious Thuret had laid the foundation of a 

 knowledge of the Nostocs ; his friend Bornet has built 

 thereon a very solid stru;ture. He has not attempted to 

 write a complete monograph of the group, inclufling there- 

 in all the "book" species, but having hal access to most 

 of the published collections of dried Algw, to the collections 

 of the Paris and Dublin Herbaria, and to the original types 

 of de Brebisson, Lenormand, Montague, Harvey, Gruno'.v, 

 and Le Jolis, he has performed wonders in the way of 

 clearing up a most tangled synonymy. 



It might shock the nerves of some botanists to recom- 

 mend that all defective descriptions of Alga;— of which no 

 original type specimens exist — ought to be overlooked. We 

 belie\e, however, that it would be for the advantage of 

 science that such a step should be taken. We may here 

 mention that the collection of Dr. Hassall, from which 

 most of the drawings of that author's " History of British 

 Freshwater Algse" were made, has been long since dis- 



persed ; so far as the Nostocs are concerned, this does not 

 much matter, as all the species were described from 

 authentic specimens still attainable. 



The Nostocs (this name is traceable to Paracelsus — • 

 "Sic etiam cjuicquid aer gignit et ex acre est vivitque 

 vel oritur ut Tereniapin, Nostoch," &c. — and yet no 

 one seems to know its meaning) are well-known plants. 

 One common species makes its appearance on lawn or 

 garden walks in summer or autumn in the form of olive 

 green (rarely bluish), irregular, and more or less shining 

 masses. It is strange to hear the guesses that are made 

 as to the nature of these. We have had them sent to 

 us as the 'peculiar spawn of earthworms," and again as 

 the eggs of some foolish frog that had mista'<en dry land 

 -for water. Some species delight in moi^t banks over 

 which water continually trickles ; some live a wholly 

 aquatic life on stones in streams. The species have an 

 enormously extended, but not yet accurately defined 

 geographical area. As to size, they vary much, some 

 being scarcely visible to the unassisted vision, some 

 forming masses as large as the upper joint of one's thumb. 



The details of such a volume as the one before us are 

 too special to be of general interest, so we rest satisfied 

 with indicating the chief confnts. The genus Nostoc is 

 treated of very fully ; the reproduction of the species by hor- 

 mogoncs and by spores is well illustrated. Instead of the 

 term trichome, we would have preferred that of filament, 

 for the former has now obtained such a common usage 

 in another sense among botanists. Despite a wonderful 

 uniformity in their structure, the spores seem to furnish 

 good diagnostic differences. It is unfortunate that they 

 are not as yet known in all the species, while in some 

 they are difficult to hit off. Twenty-nine species are formu- 

 lated. Carefully-conducted culture experiments, carried 

 on over four years, have proved that Nostoc cells found 

 within the cells of aquatic plants (Potamogeton, &c.) will 

 develop into regular Nostoc colonies, which latter have 

 been traced to the spore-producing stage. 



Four species of the genus Nodularia are described and 

 figured. This genus is better known under its more 

 familiar title of Spermosira. Nodnlaria litorea is a 

 somev.'hat remarkable species. In July, 1874, M. Cri^ 

 was commissioned to make an inquiry into the cause of 

 a noisome smell proceeding from the little lake of 

 Deauville (Calvados). It would appear that for some 

 years this district had been a regular focus of maladies, 

 and those living near it had remarked that the foetid 

 odour perceived at times came from a reddish matter 

 which periodically covered the surface of the water. M. 

 Grid soon found that this consisted of ruldy masses of 

 this Nodularian, spreading over the surface of Ruppia, and 

 that its periodic decomposition — at the moment of greatest 

 heat and lo.vest water — was the cause of the stench. The 

 perfect remedy was found in guiding a stream through the 

 little lake or pond, and thus preventing the too rapid 

 growth of the Alga 



Of the other genera treated of we must mention Lyng- 

 bya, Plectonema (for Conferva mirabilis of Dillwyn), 

 Scytonema (twenty-one species, of which a provisional 

 analysis is given. Some twenty-one species (?) are \r\- 

 eluded under 5'(y/fl;;f»/a///tvwa/i'(Kutz.), and a very impor- 

 tant Appendix gives a list of plants determined not to 

 belong to the genus, though referred to it) ; Calothrix 

 (sever il of our native species are figured and described); 

 and lastly, Gloeotrichia (of which six spe;ies are admitted). 



Enough has been wTitten to prove hov valuable an 

 addition to our works on the lower algal forms this volume 

 is. To the worker on this group— ever increasing in 

 interest — this contribution to our knowledge of it will be 

 very welcome. Such will call to mind, too, that there are 

 still lower and more confusing forms of these Algas, 

 and will be glad to hear that it is probable that the same 

 patient and clever hand hopes shortly to have reduced 

 even them to something like order. E. P. W. 



