464 



SCIENCE. 



[N. S. Vol. XII. No. 300. 



classification have assumed an altogether 

 different aspect. Affinity no longer means 

 mere similarity, but blood-relationship de- 

 pending upon common descent. We no 

 longer seek a ' system ' of classification ; 

 we endeavor to determine the mutual rela- 

 tions 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 af- 

 finities cannot be accurately estimated. If 

 the classification of Cryptogams is, at the 

 present monent, in a more satisfactory posi- 

 tion than that of Phanerogams, it is just be- 

 cause the study of the former group has 

 been, for various reasons, more thorough 

 and more minute than that of the latter. 



. PALEOPHTTOLOGY. 



The stimulating influence of the new doc- 

 trine was not, however, confined to the in- 

 vestigation 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. Mar- 

 velous progress has been made in this di- 

 rection during the nineteenth century, by 

 the labors more especially of Brongniart, 

 Goeppert, Unger, Schimper, Schenck, Sa- 

 porta, Solms-Laubach, Eenault, on the Con- 

 tinent, 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 at- 

 tempt 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 illustra- 

 tion I may adduce the statement made by 

 Mr. Clement Eeid 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 allow- 



ances for the imperfection of the geological 

 record, for the limited area investigated, 

 and for the difiiculty of determination of 

 fragmentary specimens, it may be stated 

 generally that the number of existing spe- 

 cies has been found to rapidly diminish in 

 the floras of successively older strata ; none 

 in fact, has been certainly found to per- 

 sist beyond the Tertiary period. Certain 

 existing genera, belonging to the Gymno- 

 sperms and to the Pteridophyta, have, how- 

 ever, been traced far down into the Meso- 

 zoic 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 ap- 

 parently belong, for the most part, if not al- 

 together, to the order Marattiacese, but they 

 are not referable to any of the existing 

 genera. 



Moreover, altogether new families of fos- 

 sil plants have been discovered : such are, 

 among Gymnosperms, the Cordaitacete and 

 the BennettitacCEe ; among Pteridophyta, 

 the Calamariacese, the Lepidodendracese, 

 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 Phanero- 

 gamia, Pteridophyta, Bryophyta and Thal- 

 lophyta. 



It cannot be said that the study of Paleo- 

 botany has as yet made clear the ancestry 

 and the descent of our existing flora. To 

 begin with the angiospermous flowering 

 plants, it has been ascertained that they 

 make their first appearance in the Creta- 

 ceous epoch, but we have no clue as to their 

 origin. The relatively late appearance of 

 Angiosperms in geological time suggests 

 that they must have sprung from an older 

 group, such as the Gymnosperms or the 

 Pteridophyta ; but there is no evidence to 



