TRANSACTIONS OF SECTION K. 837 



vegetation. Passing to the peninsula of India, we find the genus Glossopteris 

 abundantly represented in strata which there is good reason for regarding as homo- 

 taxial with the European Trias, and the occurrence in the same beds of some other 

 genera of Permo-Carboniferous age shows that the change in the character of the 

 southern vegetation at the close of the Palaeozoic era was much more gradual than 

 in the north. 



The comparative abundance of plant remains in the northern hemisphere in 

 rocks belonging to the Rhfetic formation, a series of sediments so named from 

 their development in the Rbaetian Alps, is in welcome contrast to the paucity of 

 the records from the underlying Triassic strata. From Virginia and adjacent 

 districts iu the United States a rich flora has been described, which by some 

 authors is assigned to the Keuper or Upper Triassic series, while others class it 

 as Rhsetic. A similar assemblage of plants is known also from the Lettenkohle 

 beds of Austria, which, as Stur has shown, clearly belong to the same period of 

 vegetation as the American tlora. We need not, however, concei-n ourselves with 

 discussions as to the precise stratigrapbical position of these American and Euro- 

 pean plant-beds, but may conveniently group together floras of Upper Triassic 

 and Rhsetic age since they exhibit but minor differences from one another. Plants 

 of Upper Triassic or Rhretic age are known from Scania and Frauconia in Europe, 

 Virginia and elsewhere in North America, Honduras, Tonkin, Australia, South 

 Africa, Chili, and other parts of the world. 



The geographical distribution of plants of approximately Rhaetic age is shown 

 in the following table on p. 838, which demonstrates an almost worldwide ran2"e of a 

 vegetation of uniform character. The character of the pbint- world is entirely ditlereut 

 from that which we have described in speaking of the Palaeozoic floras. Gymco- 

 sperms have ousted Vascular Cryptogams from their position of superiority; 

 ferns, indeed, are still very abundant, but they have undergone many and striking 

 changes, notably in the much smaller representation of the Marattiacese. The 

 Palseozoic Lycopods and Calamites have gone, and in their place we have a 

 wealth of Cycadean and Coniferous types. As we ascend to the Jurassic plant- 

 beds the change in the vegetation is comparativel)' slight, and the same persistence 

 of a well-marked type of vegetation extends into the Wealden period. It is a 

 remarkable fact that after the Palaeozoic floras had been replaced by those of the 

 Mesozoic era, the vegetation maintained a striking uniformity of character, from 

 the close of the Triassic up to the dawn of the Cretaceous era. This statement is 

 open to misconception ; I do not wish to convey the idea that a palneobotanist 

 would be unable to discriminate between floras from Rhsetic and Wealden rocks ; 

 but I wish to emphasise the fact that in spite of specific, and to a less extent of 

 generic, peculiarities, which enable us to determine, within narrow limits, the age 

 of a Mesozoic flora, the main features of the vegetation remained the same through 

 a long succession of ages. The accompanying tables (pp. S.39, 840) illustrate the 

 geographical distribution of some of the leading types of Mesozoic plants during 

 the Jurassic and Wealden periods, and demonstrate not only the striking differences 

 between the Mesozoic and Palaeozoic floras, bat also the much greater uniformity 

 in the vegetation of the world during the Secondary era than in the preceding 

 Permo-Carboniferous epoch. 



Mesozoic Floras. 



It may be of interest to glance at some of the leading types of Mesozoic floras 

 with a view to comparing them with their modern representatives. We are so 

 familiar with the present position of the flowering plants in the vegetation of the 

 world, that it is difficult for us to form a conception of a state of things in the 

 history of the plant-kingdom in which Angiosperms had no part. 



a. Conifers. 



How may we de.scribe the characteristic features of Rhsetic and Jurassic 

 floras? Gymnosperms, so far as we know, marked the highest level of plant- 

 evolution. Conifers were abundant, but the majority were not members of that 

 group to which the best known and moat widely distributed modern forms 

 belong. 



