920 REPORT — 1900. 



The development of the natural classification, of which an account has now been 

 given, proceeded for the most part on the assumption of the immutability of species. 

 As Linnaeus expressed it in his 'Fundamenta Botanica,' ' species tot numeramus, quot 

 diversse formae in principio sunt creatse.' It is difficult to understand how, with the 

 point of view, the idea of affinity between species could have arisen at all ; and yet 

 the establishment of genera and the attempts at a natural system prove tliat the 

 idea was operative. The nature of the prevalent conception of affinity is well con- 

 veyed by Linnseus's aphorism, ' Affines conveniunt habitu, nascendi modo, proprie- 

 tatibus, viribus, usu.' 



But a conviction had been gradually growing that the assumed fixity of species 

 was not well founded, and that, on the contrary, species are descended from pre- 

 existent species. This view found clear expression in Lamarck's ' Philosophie Zoo- 

 logique,' published early in the century (1809), but it did not strongly affect public 

 opinion until after the publication of Darmn's ' Origin of Species ' in 1859. Regarded 

 from this point of view the problems of classification have assumed an altogether 

 different aspect. Affinity no longer means mere similarity, but blood-relationship 

 depending upon common descent. We no longer seek a ' system ' of classification ; 

 we endeavour to determine the mutual relations of plants. The effect of this change 

 has been to stimulate the investigation of plants in all their parts and in all stages 

 of their life, so as to attain that complete knowledge of them without which their 

 affinities cannot be accurately estimated, If the classification of Cryptogams is, at 

 the present moment, in a more satisfactory position than that of Phanerogams, it is 

 just because the study of the former group has been, for various reasons, more 

 thorough and more minute than tliat of the latter. 



Palceophytology. 



The stimulating influence of the new doctrine was not, liowever, confined to the 

 investigation of existing plants ; it also gave a remarkable impulse to the study of 

 fossil plants, inasmuch as the theory of descent involves the quest of the ancestors 

 of the forms that we now have around us. Marvellous progress has been made in 

 this direction during the nineteenth century, by the labours more especially of 

 Brongniart, Goeppert, Unger, Schimper, Scheuck, Saporta, Solms-Laubach, 

 Renault, on the Continent, and in our own country of Lindley and Hutton, Hooker, 

 Carruthers, and more especially of Williamson. So far-reaching are the results 

 obtained that I can only attempt the barest summary of them. I may perhaps 

 best begin by saying that only a small proportion of existing species have been 

 found in the fossil state. In illustration I may adduce the statement made by 

 Mr. Clement Reid in his recent work, ' The Origin of the British Flora,' that 

 only 270 species, that is, about one-sixth of the total number of British vascular 

 plants, are known as fossils. Making all due allowances for the imperfection of the 

 geological record, for the limited area investigated, and for the difficulty of deter- 

 mination of fragmentary specimens, it may be stated generally that the number of 

 existing species has been found to rapidly diminish in the floras of successively 

 older strata ; none, in fact, have been certainly found to persist beyond the Tertiary 

 period. Certain existing genera, belonging to the Gymnosperms and to the Pteri- 

 dophyta, have, however, been traced far down into the Mesozoic period. Similarly, 

 the distribution in time of existing natural orders does not coincide with that of 

 existing genera; thus the Ferns of the Carboniferous epoch apparently belong, for 

 the most part, if not altogether, to the order Marattiacese, but they are not refer- 

 able to any of the existing genera. 



Moreover, altogether new families of fossil plants have been discovered : such 

 are, among Gymnosperms, the Cordaitaceoe and the Bennettitacese ; among Pteri- 

 dophyta, the Calamariacese, the Lepidodendracere, the Sphenophyllaceas, and the 

 Cycadofilices. It is of interest to note that all these newly discovered families can 

 be included within the main subdivisions of the existing flora ; in fact, no fossil 

 plants have been found which suggest the existence in the past of groups outside 

 the limits of our Phanerogamia, Pteridophyta, Bryophyta, and Thallophyta. 



It cannot be said that the study of Palseobotany has as yet made clear the 



