502 



NATURE 



[October 12, 1911 



wood, outlining an investigation on specific heats of metals, 

 especially in the neighbourhood of their melting points, and 

 determinations ol the latent heat of fusion. The metals 

 dealt with in this paper are aluminium and zinc. 



The first paper read on Wednesday was by Mr. H. 

 Davies, on the laws of solution. Mr. Davies showed how 

 the formula of Kudolphi, which had been suggested to re- 

 present the cases where Ostwald's law of dilution breaks 

 down, can be placed upon a theoretical basis. Hitherto it 

 has been held as a purely empirical formula (see in rela- 

 tion to this subject the address of the president of Section 

 B, Nature, p. 297). Mr. Davies's contribution is of great 

 importance to the physical chemist, inasmuch as it 

 elucidates " the outstanding practical problem in the 

 domain of electrolytic solutions." 



Prof. P. Y. Bevan contributed a paper on anomalous 

 dispersion and solar phenomena. If light from a non- 

 uniform source, such as an arc light, be sent through a 

 tube containing non-homogeneous vapour of a metal which 

 can show anomalous dispersion, and then an image of the 

 source be focussed on the slit of a spectroscope, an apparent 

 double reversal of certain lines may be produced. An 

 explanation is given based upon the bright images of the 

 two poles of the arc being formed on a darker background 

 of light which has come from elsewhere through the 

 vapour ; the essence of the explanation is that the source 

 shall be non-uniform. It was suggested that such apparent 

 reversals might have a bearing upon solar phenomena. 



LINKS WITH THE PAST IN THE PLANT 



WORLD. 1 

 TTNDER the heading "Links with the Past," several 

 letters were published in The Times rather more 

 than a year ago in which the writers gave instances of 

 human longevity, showing how in certain cases a chain 

 of a very few individuals suffices to connect the present 

 with a comparatively remote past. One writer, for 

 example, said that his grandmother, who died about forty 

 years ago, used to boast that her grandfather was twelve 

 years old when Charles I. was beheaded. Striking as 

 such instances are when applied to man, on the other 

 hand they serve to illustrate the relative insignificance of 

 the length of time represented by human lives as con- 

 trasted with the duration of many forest trees. It is 

 probably not an exaggeration to say that a single oak 

 tree may form a link between the present day and the 

 Norman Conquest ; a very short series of ancestors 

 suffices to carry us back to the days when the progress 

 of the Roman invaders was seriously impeded by dense 

 forests, which have long since disappeared, and farther 

 back to the age of Neolithic man, whose flint implements 

 are occasionally met with in the submerged forests round 

 our coasts. 



It would be interesting, if time permitted and my know- 

 ledge were adequate, to consider some of our forest trees 

 from the point of view of their past history. The great 

 majority of existing woods in Britain are the result of 

 cultivation, and do not come within our purview in deal- 

 ing with links with a remote past. Moreover, many of our 

 familiar British trees, such as the common elm, the lime, 

 the chestnuts, and others, have no claim to be classed as 

 native, but were introduced in Roman or post-Roman 

 days. In a few places in Inverness-shire and Perthshire 

 patches of primaeval forest survive ; one of them is repre- 

 sented by the group of Scots pines growing in the Black 

 Wood of Rannoch, in north-west Perthshire. Excavations 

 in the Scotch peat-moors have revealed a succession of 

 forests and wet moorland ; in some places, e.g. in the 

 Outer Hebrides, these buried forests occur in districts 

 which arc now almost treeless. As shown in sections 

 recently published by Dr. Lewis, a cutting through 20 

 or 30 feet of Highland peat gives us an epitome of the 

 changii and 1 limatic conditions from the close 



of the Glacial period to the present day. The remains of 

 Arctic willows, the crowberry (Empetrum nigrum), and 

 other northern species immediately above the glacial 

 deposits testify to the influence of the Ice age. The Arct it- 

 plants are succeeded by vegetation indicative of a milder 



1 Evening discourse delivered before the British Association at Ports- 

 mouth on September 4 by Prof. A. C. Seward, F.R.S. 



NO. 2189, VOL - 87] 



climate ; layers of bog-moss and stumps of pines point 

 to an alternation of forests and wet moorland. 



1 he spruce fir, one of our best known trees, affords an 

 example of a species which was once a native, but is no 

 longer found in a wild state. The cone of the spruce fir 

 shown on the screen was recently recorded by Mr. and 

 Mrs. Clement Reid, together with the seeds and fruits of 

 many other plants, from deposits on the Norfolk and 

 Suffolk coast which were formed shortly before the 

 Glacial period. The plants of this pre-glacial flora indicate 

 a temperate climate, but the nearer approach of more 

 severe conditions is shown by the Arctic willow and dwarf 

 birch which have been found in beds next above those 

 containing the spruce fir. 



The occurrence of the Glacial period is a fact of primary 

 importance in relation to the antiquity of the present flora 

 of this country. We know that Britain in comparatively 

 recent times, speaking geologically, was in very much the 

 same condition as Greenland is to-day. Over nearly the 

 whole of Scotland, Ireland, Wales, and England, with 

 the exception of a narrow strip in the south, there is clear 

 evidence of ice action on a large scale and of the presence 

 of ice-sheets and local glaciers. Under these Arctic con- 

 ditions it can hardly be doubted that only a very small 

 proportion of the vegetation could survive. Opinions differ 

 as to the extent to which the Ice age proved fatal to the 

 pre-glacial flora, but it is perhaps not too much to say 

 that the present flora, as a whole, is of post-glacial date. 

 The vegetation which grew in this part of Europe before 

 the Glacial period reached its maximum must have been 

 in great measure destroyed or driven south beyond the 

 British area. The important point is that what we call 

 our native flowering plants may safely be described in 

 general terms as immigrants from other lands, aided, it 

 may be, by land-connections across the North Sea and 

 English Channel. 



Special interest attaches to a few plants which occur 

 in the west and south of Ireland, and to a less extent 

 in Cornwall and elsewhere in the south-west of England. 

 In Connemara in the west of Ireland, where hard frosts 

 are unknown and winter snows rare, there are three kinds 

 of heath, St. Dabeoc's heath (Dabcocia polifolia), the 

 Mediterranean heath (Erica mediterranea), and Erica 

 Mackaii, which are not found elsewhere in the British 

 Isles or in the whole of northern Europe, but reappear 

 in the Pyrenees. The London pride (Saxifraga umbrosa), 

 another Pyrenean species, grows on the south and west 

 coasts of Ireland from Waterford to Donegal. Arbutus 

 Unedo (the strawberry tree), scattered through the 

 Killarney woods, has a wide distribution in the Mediter- 

 ranean region, its nearest continental station being in the 

 south-west of France. 



The presence of this small group of Mediterranean and 

 Lusitanian plants in Ireland has long been a puzzle to 

 naturalists. A few years ago I came across a solution to 

 the problem of these southern plants in Ireland in a 

 collection of stories entitled " A Child's Book of Saints." 

 An Irish monk, Bresal. was sent to teach the brethren in 

 a Spanish monastery the music of Irish choirs. In later 

 years he longed for a sight of his native land, to which 

 he at length returned : his thoughts reverted to Spain, and 

 he saw once more the little white flowers of the Saxifrage 

 and the strawberry tree from which he had gathered the 

 orange-scarlet berries. With heavenly vision the prior of 

 the Spanish monastery, seeing Bresal gazing at the flowers 

 of Spain, commanded them to go and make real his dream. 

 Thus, to gladden the heart of the monk, were these 

 southern plants miraculously introduced into Ireland. 



One view is that Arbutus and its companions are 

 entitled to be regarded as a very old section of the British 

 flora, survivals from a time, the so-called Tertiary period, 

 when the climate was much milder than it is to-day. It 

 is believed by some authorities that these plants migrated 

 from Portugal to Ireland long before the Glacial period, 

 and by means of a land-bridge, which afterwards sank 

 below the waters of the Atlantic Ocean. This explanation 

 is open to criticism ; even granting the former existence 

 of a land-connection, it is difficult to believe that the 

 strawberry tree, which is restricted to one of the warmest 

 districts in the British Isles, could have survived the 

 rigours of the Glacial period. Moreover, as Mr. Clement 



