Septembee 28, 1900.] 



SCIENCE. 



465 



definitely establish either, of these possible 

 origins. Then as to the origin of the Gym- 

 nosperms, whilst it cannot be doubted that 

 they were derived from the Pteridophyta, 

 the existing data are insufBcient to enable 

 us to trace their pedigree. The most an- 

 cient family of Gymnosperms, the Cordait- 

 acese, can be traced as far back as any 

 known Pteridophyta, and cannot, therefore, 

 have been derived from them ; but the fact 

 that the Cordaitacese exhibit certain cyca- 

 dean affinities, and the discovery of the 

 Cycadofilices, suggest that what may be 

 termed the cycadean phylum of Gymno- 

 sperms (including the Cordaitacete, Ben- 

 nettitacese, Cycadacese, and perhaps the 

 Ginkgoacese) had its origin in a filicineous 

 ancestry, of which, it must be admitted, no 

 forms have as yet been recognized. 



Turning to the Pteridophyta, the origin 

 of the Ferns is still quite unknown : the one 

 fact which seems to be clear is that the eu- 

 sporangiate forms (Marattiacese) are more 

 primitive than the leptosporangiate. With 

 regard to the Equisetinse, the Calamariacese 

 were no doubt the ancestors of the existing 

 and of the fossil Equisetums. Similarly, in 

 the Lycopodinse, the paleozoic Lepidoden- 

 dracece were the forerunners of the existing 

 Lycopodiums and Selaginellas. The dis- 

 covery of the Sphenophyllacese seems to 

 throw some further light upon the phylog- 

 eny of these two groups, inasmuch as these 

 plants possess characters which indicate 

 afiinity with both the Equisetinse and the 

 Lycopodinse, thus suggesting the possibility 

 that they may have sprung from the same 

 ancestral stock. 



To complete the geological survey of the 

 vegetable kingdom I will briefly allude to 

 the Bryophyta and the Thallophyta. Ow- 

 ing no doubt to their delicate texture, the 

 records of these plants have been found to 

 be very incomplete. So much is this the 

 case with the Bryophyta that I forbear to 

 make any statement concerning them. The 



chief point of interest with regard to the 

 Fungi is that most of those which hav& 

 been discovered in the fossil state were- 

 found in the tissues of woody plants on 

 which they were parasitic. In this way it 

 has been possible to ascertain, with some 

 probability, the existence of Bacteria and of 

 mycelial Fungi in the Paleozoic period. 

 The records of the Algfe are more satis- 

 factory ; they have been traced far back 

 into the Paleozoic age, where they are rep- 

 resented by siphonaceous forms and by the 

 somewhat obscure plants known as Nemato- 

 phycus and Pachytheca. 



In a general way the study of Paleobot- 

 any has proved the development of higher 

 from lower forms in the successive geolog- 

 ical periods. Thus the Tertiary and Quat- 

 ernary periods are characterized by the 

 predominance of Angiosperms, just as the 

 Mesozoic period is characterized by the pre- 

 dominance of Gymnosperms, and the Pale- 

 ozoic by the predominance of Pteridophyta. 

 And yet, as I have been pointing out, we 

 are not able to trace the ancestry of any one 

 of the larger groups of plants. The chief 

 reason for this is that the geological record, 

 so far as it is known, has been found to 

 break off with such surprising abruptness 

 that the earliest, and, therefore, the most 

 interesting, chapters in the evolution of 

 plants are closed to us. After the wealth 

 of plant-forms in the Carboniferous epoch 

 there is a striking falling- off in the De- 

 vonian, in which, however, plants of high 

 organization, such as the Cordaitacese, the 

 Calamariacese and the Lepidodendracese, 

 still occur. In the Silurian epoch vas- 

 cular plants are but sparingly present — 

 but it is remarkable that any such highly 

 organized plants should be found there 

 — together with probable Algse, such as 

 Nematophycus and Pachytheca. The Cam- 

 brian rocks present nothing but so-called 

 ' Fucoids,' such as Eophyton, etc., some of 

 which may be Algae. The only known fos- 



