462 



NA TURE 



{Sept. ii, 1 J 



bridge, and who was excellently qualified for the task, 

 should take Sullivant's place in the undertaking, but he 

 died in 1882, and Lesquereux, in old age with his sight fail- 

 ing, was again left alone. The book might have altogether 

 collapsed if it had not been for the kind intervention of 

 Dr. Sereno Watson, who now has charge of the Harvard 

 Herbarium, and who, although not specially a bryologist, 

 has taken upon himself the needful critical and editorial 

 labour that was required to complete it. 



The book as now published includes all the mosses 

 which are known on the North American continent within 

 the limits of the United States and northwards. There 

 is already a " Manual of the Moss es of Tropical America," 

 by Mitten, in the twelfth volume of the Journal of the 

 Linnean Society, and there are special monographs by 

 Bescherelle on the mosses of Mexico and the West 

 Indies. Sullivant has published figures of most of the 

 endemic types, and Drummond, Austin and Sullivant and 

 Lesquereux have issued extensive sets of dried specimens 

 with numbers and printed labels. In the present work 

 900 species are included. A very large proportion of 

 them are European, and as the close identity of the moss- 

 flora of the temperate zone in the two continents is so 

 interesting and important from a geographical point of 

 view, we should have been glad if the example of Dr. 

 Gray in marking those species which are common to 

 Europe and America had been followed. Of the six 

 plates five are those which were sketched out by Sullivant, 

 and the sixth is devoted mainly to the sections of Hypnum. 

 The classification does not differ materially from that of 

 Bruch and Schimper, familiar to us in England from 

 being used in Wilson's " Bryologia." The definitions of 

 species and genera are commendably full and clear, and 

 in not establishing or admitting species upon a slender 

 foundation of differential character, the authors have 

 followed the excellent example that has made Dr. 

 Gray's manual, which has now reached its fifth edition, 

 one of the most popular and practically useful of botanical 

 handbooks. 



At the end there is a useful glossary of the technical 

 terms used in the descriptions. As it is such a good and 

 cheap book and includes such a large proportion of the 

 British species, it is well worthy of the attention of our 

 home collectors. J. G. Baker 



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 . 



[7 lie Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressztre on his space is so great 

 that it is impossible otherwise to insure the appearance even 

 of communications containing interesting and novel facts.] 



The Diffusion of Species 



During a recent cruise among the Hebrides two circum- 

 stances came before me, both of which are of some interest in 

 natural history — one of them illustrating the curious conditions 

 attending the diffusion of species, and the other illustrating the 

 not less curious conditions affecting the multiplication of par- 

 ticular species in particular seasons. 



The celebrated Island of Iona is separated from the nearest 

 part of the Isle of Mull by a sound which is three-quarters of a 

 mile wide. It is the channel of very strong tidal currents, and 



when the winds blow in certain directions a heavy sea runs 

 through it. This sound has been an effectual isolater of Iona 

 from the access of several species common in Mull. Among 

 others are to be numbered snakes and other reptiles. Tradition 

 ascribes the immunity of the sacred isle to the blessing of St. 

 Columba. Certainly it has been complete. Yet, strange to 

 say, this immunity has been this year endangered. During the 

 late very hot August an adder attempted the passage to Iona, 

 and was in the act of effecting a successful landing, when, 

 fortunately, it was seen by a boy and a girl who were occupied 

 among the stones on the sea-shore. The adder was tired by its 

 long swim, and the boy killed it without difficulty by stamping 

 on its head. This is surely a very curious case of migration ; 

 and it is difficult to conceive the impulse und.-r which the snake 

 committed itself to the tides and currents of a channel so broad 

 and dangerous. The hot weather of this year has no doubt 

 developed in all reptiles an abnormal activity ; and I saw a 

 youth in Mull who had recently very nearly lost his life from the 

 bite of an adder. The description given me of his condition for 

 many hours brought home to my mind almost for the first time 

 that we have in our own island a veritable member of the terrible 

 "Thanatophidia." But it seems quite unaccountable why 

 such a reptile should have attempted to cross the Sound of 

 Iona. 



The other circumstance to which I have referred is the mar- 

 vellous development of the Salpida? this year in the Ilebridean 

 seas. I have cruised on tho=e seas every year for fifteen year, 

 regularly, and I have been often on the look-out for these curious 

 organisms ; yet I have never seen them at all except once, and 

 then only rarely and locally. Whereas this year the water was 

 laden with them almost everywhere, and in some places it was 

 rendered almost foul with their enormous quantity. In the 

 Sound of Iona my tow-net was soon half filled with them ; 

 and the long chains of beautiful pattern which passed under the 

 yacht lent an additional charm to the exquisite colour of that 

 pure oceanic water. In the Sound of Raasay, near Portree, the 

 number was still greater. But the maximum development ap- 

 peared in Loch Scavaig, where, as far down as the eye could 

 reach, 'here was nothing to be seen but Salpas in every variety 

 of concatenation and decatenation — long chains, short chains, 

 and countless myriads of separated individuals — making the 

 whole sea little more than a thick soup of Salpse. 



On being placed in a glass of water the muscular contractions 

 of their bodies were beautifully exhibited, and their darting 

 movements were very striking. Their exquisite crystalline mate 

 rial allowed every detail of structure to be seen ; and on being 

 placed in numbers in a bucket of water, and on being stirred at 

 night, their phosphorescence was brilliant. 



I should be glad to know from any of your correspondent- 

 whether there is any explanation of this exceptional development 

 of these creatures. Argyll 



Inveraray, September 6 



Meteor- Moon- and Sun-Shine 



Descending the Calton Hill from the Royal Observatory on 

 Tuesday night, I was much struck with the appearance, though 

 momentary only, of a fine meteor of Venus-like brightness, pass- 

 ing in a short course from south-east to north-east nearly hori- 

 zontally, and at a height of about half a degree above the 

 Pleiades, at 3 minutes past 12 G.M.T. The yellowness of the 

 meteor's light was very conspicuous, contrasted with theblueness 

 of the faint stars and nf the sky about them in that direction, 

 shimmering in pale blue reflected moonlight ; and seemed to 

 speak of abundance of sodium, as well as a low temperature of 

 incandescence, in that particular meteor. 



But very different was the colour in the opposite quarter of 

 the sky, or just west of south, where the moon, within a day of 

 the full, was shining brilliantly, in white light immediately 

 around and above it, but producing between it and the horizon, 

 and for a considerable distance on either side, exactly and most 

 perceptibly that faintly claret-coloured haze, which I have been 

 remarking about and beneath the sun all this year. Precisely 

 too as with the sun, the colour was shown on this occasion with 

 the moon to be in the very highest regions of the atmosphere 

 by any cumulus clouds, at heights of 3000 or 4000 feet, that 

 floated past, being pre-eminent on that warm-coloured backing, 

 by the pearly whiteness of their lights and blueness of their 

 shadows. In so far quite agreeably with Mr. Backhouse's recent 

 and very interesting letter in NATURE (p. 359), stating thatdie had 



