582 



NATURE 



[October 15, 1891 



on account of their superficial resemblance to the spore-tetrads 

 of the higher Cryptogams. The carpospores, which are the real 

 sexual products, he regarded as gemmte like those of Marchantia, 

 with the cups of which he compared the cystocarps. Such views 

 were excusable at that time, but Nageli, as we shall see, adhered 

 to them later on with excessive pertinacity. 



Nageli was perfectly acquainted with the conjugation _ of 

 Desmids and Zygnemacese and imperfectly with the fertilization 

 of Vaucheria, but he imagined that these processes were too in- 

 constant to be regarded as sexual, 



Nageli was at that time much more successful in dealing 

 with the vegetative organs of the Algae, and he rightly protested 

 against the generalization current down to our own day, that 

 all Algae are destitute of leaves. 



His conviction that the Algse are without exception sexless 

 led him in 1849 to reject Decaisne and Thuret's discovery of the 

 spermatozoids of Fucus, which he regarded as spores. Of his 

 later algological papers, the most important is that on the 

 Ceramiaceae, published in iJ^6i. In this the procarpia and 

 trichogynes, the true female organs, are described and accurately 

 figured ; but Nageli failed to recognize their true nature, and 

 still maintained his old view of the sexuality of the tetraspores. 

 The whole credit of the discovery of the real state of the case 

 thus belongs to the French botanists Thuret and Bornet. 



The " Pflanzenphysiologische Untersuchungen " of Nageli and 

 Cramer (1855-8) contain among other papers of importance 

 Nageli's huge work on starch grains (about 6co quarto pages !), 

 which is of great general value as embodying his views on the 

 growth of starch and cell-wall by intussusception and on the 

 molecular structure of organized bodies. For many years this 

 micellar theory, as it was afterwards called, was regarded as 

 Nageli's greatest achievement. Sachs, in 1875, said in his 

 " History of Botany" : " Nageli's molecular theory is the first 

 successful attempt to apply mechanico-physical considerations to 

 the explanation of the phenomena of organic life." More 

 recent research has shown that this attempt, like its predecessors, 

 was premature, and though Nageli's ingenious and carefully 

 elaborated hypotheses must still arouse our admiration, we can 

 scarcely now regard them as having added much to our know- 

 ledge either of the growth or structure of organized bodies. 

 The book on " Starch Grains," however, quite apart from 

 theoretical considerations, will always remain a marvellous 

 monument of research. It contains a vast mass of systematic 

 and descriptive matter in addition to the speculations which 

 have made it famous. The micellar theory was further de- 

 veloped in subsequent papers "on the behaviour of polarized 

 light towards vegetable organisms" (1862); "on crystalloid 

 protein bodies" (1862); and "on the internal structure of 

 vegetable cell-membranes" (1864). It is presented in its 

 perfected form in the important work on the microscope, pub- 

 lished by Nageli and Schwendener in 1877. 



The papers in the " Physiologische Untersuchungen " bear the 

 name of Nageli or of Cramer respectively, but it appears that 

 they mutually assisted each other throughout ; hence it is not 

 out of place to mention here Cramer's fine researches on the 

 apical growth of Equisetum, which to this day serve as a 

 model (rarely approached) for all such investigations. 



No sooner were these investigations with Cramer completed 

 than another great undertaking was commenced in the publica- 

 tion of the "BeitragezurWissenschaftlichen Botanik" (1858-68). 

 This began with the great paper " On the Growth of Stem and 

 Root in Vascular Plants and on the Arrangement of the Vascular 

 Bundles." This is the most important of Nageli's purely ana- 

 tomical works, and is of the greatest permanent value. It is 

 not too much to say that the bulk of our knowledge of the dis- 

 tribution of vascular tissues in plants still depends on this work. 

 Other valuable papers in the " Beitrage " are those on the use of 

 the polarizing microscope, on the growth in thickness of the 

 Sapindacese (another ideal pattern of anatomical research), and 

 on the origin and growth of roots, in which last Leitgeb co- 

 operated. Until the quite recent work of Van Tieghem and 

 Douliot, this was undoubtedly the most important investigation 

 on the subject. 



Among Nageli's later works there are two which have had a 

 lasting influence on our views as to the biology and physiology 

 of the simplest plants. In "Die niederen Pilze " (1877) he 

 treats of moulds, yeasts, and bacteria in relation to infectious 

 diseases and hygiene. In this work an excessive scepticism is 

 displayed as to the existence of definite species among the 

 lowest organisms, such a> bacteria. There is no longer any 



NO. 



II 46, VOL. 44] 



doubt that species are neither more nor less distinct among 

 these simple beings than among the higher plants, hut Nageli 

 did a real service in showing that each of these species may 

 appear in a number of morphologically and physiologically 

 different form?. 



Nageli's " Theorie der Gahrung " (1879) demonstrated the 

 relation between the processes of fermen ation and respiration, 

 and established the modern view of fermentation, according to 

 which, to use the words of Prof. Vines, "living protoplasm, 

 besides undergoing decomposition itself, can induce decomposi- 

 tion in certain substances which are brought within the sphere 

 of its influence." 



It remains to consider briefly an aspect of Nageli's work, 

 which is from some points of view the most interesting of all — 

 namely, his relation to the theory of descent. The elaborate 

 observations on variable species, especially in the genus Hiera- 

 cium, which Nageli carried on throughout his whole life, side by 

 side with his histological and physiological work, specially 

 qualified him to take up an independent position with reference 

 to the problems of evolution. 



In his paper " Die Entstehung und BegrifF der naturhistor- 

 ischen Art " (1865), Nageli for the first time discusses this 

 question in the light of Darwin's work. His belief, however, 

 in the origin of species by descent was no new thing, but had 

 been tacitly held by him throughout his whole scientific career, 

 and had been definitely expressed in his paper on individuality 

 in Nature, published in 1856. In his work of 1865 he gave an 

 admirably clear exposition of natural selection, but was unable 

 to accept it as affording a sufficient explanation of evolution. 

 He believed that variation has a definite direction, always tend- 

 ing towards the greater complexity and perfection of the organism 

 (Vervollkommnungstheorie). On this view the development of 

 the race, like that of the individual, has a definite course as- 

 signed to it beforehand. He protests that there is nothing 

 supernatural involved in this doctrine, and that it does not 

 necessarily require sudden transformations. On this latter 

 question, however, he speaks very uncertainly, and states that 

 transitions between certain morphological types appear to be 

 unthinkable and impossible. One seems to catch here an echo 

 of his older teaching about the " Absolutheit der Begriffe." 



■ The perfecting process, he says, knows no rest ; hence all 

 plants would have become Phanerogams by this time were it 

 not that spontaneous generation takes place at all periods. 

 Thus the flowering plants of our own day have, on this view, 

 the longest family history, and trace their descent from the first- 

 formed " Urzellen," while the vascular cryptogams had a some- 

 what later origin, and have, consequently, not had time 10 

 advance so far, the mosses again arose more recently still, and 

 so on with all the groups of plants. According to this singular 

 hypothesis, there is no actual blood relationship between the 

 higher and lower forms of any one epoch. They have had a 

 similar but not a common origin. This remarkable, but, as it 

 seems to us, retrogressive theory was maintained by Nageli to 

 the close of his career. 



But, whatever view may be taken of this speculation, it must 

 be admitted that Nageli saw clearly the great fact — since brought 

 home to us by the works of Weismann and his school— that 

 the causes of variability are internal to the organism. This 

 important doctrine, based on original experiments and observa- 

 tions, is maintained in a paper entitled " Ueber den Einfluss 

 ausserer Verhaltnisse auf die Varietatenbildung im Fflanzen- 

 reiche" (1865). He shows that " the formation of the more or 

 less constant varieties or races is not the consequence and the 

 expression of external agencies, but is determined by internal 

 causes " ; while the modifications directly produced by external 

 influences are inconstant, and do not give rise to varieties. We 

 think it must be allowed that, on this essential point, Nageli 

 was at that time somewhat in advance of Darwin himself. 



Other works of that period deal with the laws affecting the 

 distribution of species, and with the phenomena of hybridiza- 

 tion. In the " Theorie der Bastardbildung" (1866) the pecu- 

 liarities of hybrids are explained as due to the favourable or 

 unfavourable changes produced by crossing, in the internal 

 coadaptation of the organs of the offspring. 



A paper on the social origin of new species (1872) results in 

 the conclusion that groups of new torms are likely to arise 

 simultaneously, rather than isolated new species. 



Finally, something must be said of the great work published 

 in 1884, " Die mechanisch-physiologische Theorie der Abstam- 

 mungslehre," which states at great length Nageli's final con- 



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