1 8 PROCEEDINGS OF THE 



felt the same nood for Ji better basis of comparison. He says, 

 "The wbole Anatomy of the Plant must be studied," and cites 

 Cuvier's famous researches on fossil animals as a model. This 

 lieultliy reaction of fossil work on the investigation of living 

 ])lants still goes on in our own dny. 



JJroiigniart gives an excellent account of ilie characters available 

 for the discrimination of fragmentary specimens, and points out 

 that while almost any organ will sudice to distinguish the main 

 groups, for more exact determination the vegetative organs have a 

 relatively greater importance in the lower and the re})roductive in 

 the higher classes. At the same time, the signitic-ance of vascular 

 anatomy had long been recognised in the distinctive characters of 

 Dicotyledons and Monocotyledons. " After the internal structure 

 of the stem," he says, " the most important character of this organ 

 is the mode of insertion of the leaves on its surface," then the 

 arrangement of the vessels passing from the stem into the petiole, 

 and in the leaves themselves the venation. We see that Brong- 

 niart, poorly provided at that time with structural material, was 

 feeling about after external characters which might serve as the 

 " outward and visible sign " of the structure within. 



Comparative anatou)y, he argues, forms the basis of zoological 

 classification, and it will be tiie same for plants, only here the 

 difficulty is greater, because a more or less high ningnification is 

 always required to show the structure. He especially regrets the 

 absence, at that time, of any comparative anatomy of the wood, 

 a need which even now has scarcely been adequately supplied. 

 Let us see, a little more in detail, how Brongniart succeeded ia 

 applying his principles to the problems of fossil botany. 



He recognised four periods of geological time, in which the 

 vegetation had a special aspect due to the predominance of certain 

 families and to the great development of the plants of these 

 families. This recognition of successive periods of vegetation 

 was in itself a great step in advance. Only a few years before, 

 botanists had still expected to be able to refer the fossils of the 

 Coal to recent species and appeared disaj)pointed when thej failed 

 to do so. The same spirit still sometimes shows itself in our own 

 day, among those who view anything like an intermediate fossil 

 group with suspicion. Brongniart's four periods (characterised 

 in his own words) were :— 



1. Vegetation almost solely composed of Ferns and ai'borescent 



Horsetails and of the singular Lepidodendrons — gigantic 

 plants sharing in the characters of Lycopods and Conifers. 

 After the first period these plants seem to have disappeared, 

 at least from the regions so far explored. 



2. Characterized by very different forms, of which only a small 



number has come down to present times, — they are espe- 

 cially Ferns, less elevated than those of the Coal, and 

 Conifers of a very peculiar aspect. 

 [This refers essentially to the Triassic Flora.] 



