3IO 



NA TURE 



IJuly 25, 1889 



signification I have not been able to find out. The mist is 

 popularly supposed to come from the sea, but this is only partly 

 true. The fog doubtless rolls from the west or seaward side, but 

 the origin is certainly due to local radiation, for the densest 

 mist may lie over the Pampa, when there is no trace of fog on 

 the sea-coast. 



The nights and forenoons are usually calm on the Pampa, but 

 about I p.m. a moderate wind springs up from the south-west, 

 which falls away at sunset. During the night a light air some- 

 times blows from the Cordillera ; and if the wind comes from the 

 east, the camancliaca is immediately evaporated. 



The Sierra or Cordillera is strangely enough governed by a 

 totally different weather system from that of the coast ; for it 

 rains heavily in the mountains during the summer months of 

 December, January, or February ; and I have been assured that 

 whenever it does rain on the Pampa, the precipitation has been 

 blown over from the Sierra. The extreme dryness of the Pampa 

 is owing to its geographical position between the coast range, whose 

 scanty rainfall occurs in zvinter, and the Sierra, where heavy rain 

 falls in summer, but the precipitation of neither reaches the plain, 

 which therefore remains a desert. My own observations on the 

 surface and upper winds along the whole length of the Andes, 

 from Valparaiso to Lima, prove conclusively that the old theory 

 that the dryness of the west coast of South America is due to 

 the south-east trade rising over the Andes, and then descending 

 as a warm dry current, is totally wrong, for I found all the 

 winds over 10,000 feet, either from north-east or north-west. 



The Pampa is very healthy, for fever is unknown, and though 

 the heat and drought sometimes affect the liver, and a mild 

 dysentery sometimes shows itself, still both are very amenable to 

 proper treatment. There seems to be only one ailment special 

 to the Pampa and the other nearly rainless districts of South 

 America. This is the so-called "barley blindness" of mules 

 and horses, which manifests itself by a white growth on the pupil 

 of the eye. Absence of sufficient moist food is said to be the 

 cause of this malady, and there is no doubt that if removed in 

 time to a natural pasturage, the affected animal soon more or less 

 recovers its sight. Ralph Abercromby. 



FOR TUITO US VARIA TION. 



A T a meeting of the Biological Society of Washington (United 

 -^ *" States), held on December 15, 1888, Mr. Lester F. Ward 

 read a paper on "Fortuitous Variation, as illustrated by the 

 genus Eiipatorium." He exhibited a series of specimens of that 

 genus, mostly from the vicinity of Washington, and growing in 

 great part in the same kind of soil and under the same general 

 conditions. To simplify the question, the differences in the 

 flowers, heads, and reproductive parts in general, which are less 

 marked in this than in almost any other genus, were ignored, 

 and attention was exclusively directed to the leaves. These, 

 when closely compared, are seen to differ considerably in the 

 different species, the forms ranging from the filiform dissected 

 leaves of E. fivniculaceum to the broad ovate leaves of E. 

 ageratoides. But between these extremes there are represented 

 in the Washington flora numerous much more similar forms, 

 which present to the observer a strongly marked family re- 

 semblance ; from those with more elongate leaves, such as E. 

 altissimiun, E. album, and E. teucrifolium, through the in- 

 creasingly broader more ovate forms, E. perfoliattim, E. sessili- 

 folium, and E, rotundifolium ovatum {E. pubescens, Muhl. ), with 

 an intermediate undescribed form, which Dr. Gray regarded as a 

 hybrid, connecting the last two to the typical E. rotundifolium, 

 with its roundish, crcnate, but still sessile leaves ; and from this 

 last form, with several similar Mexican species, on in the direc- 

 tion of acquiring a petiole, through several exotic forms, to E. 

 cxlestinum, E. aromaticum, and E. agcratoides, in an almost 

 unbroken chain of modifications without any apparent advantage 

 to the plants. Almost any other genus might have served the 

 purpose of the paper, but this one seemed to possess the merit 

 of simplicity. 



The question naturally arises, in looking at such a group of 

 clearly related forms, all of which, on the modern view, must 

 S-irely have descended from some common ancestral stock, Why 

 have they varied at all ? Why need there be more than one 

 syecies of Eupatorium in the same restricted flora ? Or, if some 

 c m be shown to have probably varied in order to adapt them- 

 salves to different local conditions, why need there be more 

 than one form occurring under precisely the same conditions ? 

 Variation caused by natural selection can only occur where some 

 advantage is secured through it, whereby the new form becomes, 



by ever so little, better fitted to survive under the conditions of 

 its existence. But here there seems to be no such advantage. 

 It is easy to say that we are incapable of detecting the subtle 

 influences that make one form surer of existence than another. 

 The staunch believer in natural selection may be satisfied with 

 such an explanation, but is it not too much to a?k of the new 

 convert or the sceptic ? Is not the spread of the doctrine 

 hindered rather than helped by such a demand? Moreover, it 

 was shown that several different forms actually flourish together 

 in the very same localities, and that this is not exceptional, but 

 the common case, so that the idea of special fitness of form to 

 station is precluded. And is it not antecedently improbable 

 that there should be any advantage in a plant's having a sharp- 

 pointed rather than a blunt-pointed leaf, a serrate rather than 

 a crenate one, or a sessile rather than a short-petioled one? 

 Science becomes metaphysics when such questions are discussed. 



The speaker proposed to escape from the dilemma by denying 

 that advantage, cr fitness to survive, or natural selection, had any- 

 thing to do with such variations ; and he maintained that they 

 were truly fortuitous in the only true sense of that term. By this 

 he did not mean to say that they were due to mere chance in the 

 sense of being without cause ; and the remainder of his paper 

 was devoted to an attempt to explain the cause of fortuitous 

 variation. It may be briefly summed up as follows : — 



Organized or living matter con-^tantly tends to increase in 

 quantity, which may be regarded as the true end of organic 

 being, to which the perfection of structure, commonly mistaken 

 for such end, is only one of the means. Every organic element 

 may be contemplated as occupying the centre of a sphere, toward 

 the periphery of which, in all directions alike, it seeks to expand, 

 and would expand but for physical obstructions which present 

 themselves. The forms which have succeeded in surviving are 

 those, and only those, that were possible under existing con- 

 ditions ; that is, they have been developed along the lines of 

 least resistance, pressure along all other lines having resulted in 

 failure. Now, the various forms of vegetable and animal life 

 represent the latest expression of this law, the many possible, 

 and the only possible, results of this universal nisus of organic 

 being. The different forms of Eupatorium, or of any other 

 plant or animal, that are found co-exisling under identical 

 conditions merely show that there were many lines along which 

 the resistance was not sufficient to prevent development. They 

 are the successes of Nature. 



Mr. Ward disclaimed any desire to discredit or impair in any 

 way the great law of natural selection. The most important 

 variations, those which lead up to higher types of structure, are 

 the result of that law, which therefore really explains organic 

 evolution ; but the comprehension and acceptance of both 

 natural selection and evolution are retarded instead of being 

 advanced by claiming for the former more than it can explain, 

 and it might as well be recognized first as last that a great part 

 — numerically, by far the greater part — of the variety and multi- 

 plicity, as well as the interest and charm, of Nature is due to 

 another and quite distinct law, which, with the above qualifica- 

 tions, may perhaps be appropriately called " the law of fortuitous 

 variation." 



SCIENTIFIC SERIALS. 



American Journal of Science, July. — A new Erian (Devonian) 

 plant allied to Cordaites, by Sir William Dawson. This unique 

 specimen from the lower Catskill (Upper Devonian), Wyoming 

 County, Pennsylvania, presents the peculiarity of combining the 

 fructification of the Cordaitese with foliage akin to that of 

 Nreggerathia, thus connecting two Palaeozoic groups which are 

 now considered as allied to Cyadese and Taxineas. — The law of 

 thermal relation, by William Ferrel. The object of these re- 

 searches is to compare Dulong and Petit's older formulae and the 

 more recent determination of Stefan with the principal available 

 data derived from experiment and observation, with a view to 

 ascertaining what modifications these formula; may require in 

 order accurately to represent the true law of relation between 

 the intensity of the radiation and the temperature of a body. 

 It appears generally that neither of the formula; in question 

 represents the true law of Nature through the whole range of 

 experiments, but that different values are required for different 

 ranges of temperature. To determine the true mean value with 

 greater accuracy experiments upon radiation will have to be made 

 at much lower temperatures than any yet made.— Stratigraphic 

 position of the Olenellus fauna in North America and Europe 

 (continued), by Charles D. Walcott. Since writing the first part 



