176 .ANCIENT PLANTS 



necessary to have an elaborate training in the structure 

 of living ones. In the preceding chapters only the salient 

 features have been considered, so that from them we can 

 only glean a knowledge similar to the picture of a house 

 by a Japanese artist — a thing of few lines. 



Even from the facts brought together in these short 

 chapters, however, it cannot fail to be evident how large 

 a field fossil botany covers, and with how many subjects 

 it comes in touch. From the minute details of plant 

 anatomy and evolution pure and simple to the climate 

 of departed continents, and from the determination of 

 the geological age of a piece of rock by means of a 

 blackened fern impression on it to the chemical ques- 

 tions of the preservative properties of sea water, all is 

 a part of the study of "fossil botany". 



To bring together the main results of the study in 

 a graphic form is not an easy task, but it is possible to 

 construct a rough diagram giving some indication of the 

 distribution of the chief groups of plants in the main 

 periods of time (see fig. 122). 



Such a diagram can only represent the present state 

 of our imperfect knowledge; any day discoveries may 

 extend the line of any group up or down in the series, 

 or may connect the groups together. 



It becomes evident that so early as the Palaeozoic 

 there are nearly as many types represented as in the 

 present day, and that in fact everything, up to the 

 higher Gymnosperms, was well developed (for it is hard 

 indeed to prove that Cordaites is less highly organized 

 than some of the present Gymnosperm types), but 

 flowering plants and also the true cycads are wanting, 

 as well as the intermediate Mesozoic Bennettitales. 

 The peculiar groups of the period were the Pterido- 

 sperm series, connecting links between fern and cycad, 

 and the Sphenophyllums, connecting in some measure 

 the Lycopods and Calamites. With them some of the 

 still living groups of ferns, Lycopods, and Equisetaceae 

 were flourishing, though all the species differed from 



