Sbptembee 28, 1900.] 



SCIENCE. 



463 



erogames gymnospermes'; and although the 

 systematic position of these plants has since 

 then been the subject of much discussion, 

 the recognition of the Gymnospermse as a 

 distinct group of archaic Phanerogams is 

 now definitely accepted. 



Moreover, the greatly increased knowl- 

 edge of the Cryptogams has involved a con- 

 siderable reconstruction in the classification 

 of that great sub-kingdom. One of the 

 most striking discoveries is that first defi- 

 nitely announced by Schwendener (1869) 

 concerning Lichens, to the efiect that the 

 body of a Lichen consists of two distinct or- 

 ganisms, an Alga and a Fungus, living in 

 symbiosis ; a discovery which was so nearly 

 made by other contemporary botanists, such 

 as de Bary, Berkeley, and Sachs, and which 

 can be traced back to Haller and Gleditsch 

 in the eighteenth century. 



But the discoveries which most affected 

 the classification of the Cryptogams are 

 those relating to their reproduction. Whilst 

 it had been recognized, almost from time 

 immemorial, that Phanerogams reproduce 

 sexually, sexuality was denied to Crypto- 

 gams until the observations on Liverworts 

 and Mosses by Schmidel and by Hedwig 

 (of whom it was said that he was born to 

 banish Cryptogamy) in the eighteenth cen- 

 tury ; and even as late as 1828 we find 

 Brongniart classifying the Fungi and Algae 

 together as'Agames.' But in the middle 

 third of the nineteenth century, by the 

 labors of such men as Thuret, Pringsheim, 

 Cohn, Hofmeister, ISTaegeli, and de Bary, the 

 sexuality of all classes of Cryptograms was 

 clearly established. It is worthy of note 

 that, although the sexuality of the Phaner- 

 ogams had been accepted for centuries, yet 

 the details of sexual reproduction were first 

 investigated in Cryptogams. For it was 

 not until 1823 that Amici discovered the 

 pollen-tube, and it was more than twenty 

 years later (1846) before he completed his 

 discovery by ascertaining the true signifi- 



cance of the pollen-tube in relation to the 

 development of the embryo ; whilst it re- 

 mained for Strasburger to observe, thirty 

 years later, the actual process of fertilization. 



The discovery of the reproductive proc- 

 esses in Cryptogams not only facilitated a 

 natural classification of them, but had the 

 further very important effect of throwing 

 light upon their relation to Phanerogams. 

 Perhaps the most striking botanical achieve- 

 ment of the nineteenth century has been the 

 demonstration by Hofmeister's unrivaled 

 researches (1851) that Phanerogams and 

 Cryptogams are not separated, as was for- 

 merly held, by an impassable gulf, but 

 that the higher Cryptogams and the lower 

 Phanerogams are connected by many com- 

 mon features. 



The development of the natural classifi- 

 cation, of which an account has now been 

 given, proceeded for the most part on the 

 assumption of the immutability of species. 

 As Linnseus expressed it in his ' Funda- 

 menta Botanica,' ' species tot numeramus, 

 quot diversse formse in principio sunt cre- 

 atse.' It is diiScult to understand how 

 with the point of view, the idea of afiinity 

 between species could have arisen at all ; 

 and yet the establishment of genera and 

 the attempts at a natural system prove that 

 the idea was operative. The nature of the 

 prevalent conception of affinity is well con- 

 veyed by Linnseus's aphorism, ' Affines con- 

 veniunt habitu, nascendi modo, proprieta- 

 tibus, veribus, usu.' 



But a conviction had been gradually 

 growing that the assumed fixity of species 

 was not well founded, and that, on the con- 

 trary, species are descended from preexist- 

 ent species. This view found clear expres- 

 sion in Lamarck's ' Philosophic zoologique, ' 

 published early in the century (1809), but 

 it did not strongly affect public opinion 

 until after the publication of Darwin's 

 ' Origin of Species ' in 1859. Eegarded 

 from this point of view the problems of 



