KESULTS OF PAL^EONTOLOGICAL KESEARCH 65 



which the Lepidophytes, or the Equisetae for instance, 

 experienced in the course of geological periods represent 

 a simple change of form, a specialization of one and 

 the same grade of organization in varied directions. 

 The reasons for this we will at once present. 



3. Description of changes actually observed and the 

 probable causes of same (' Palceontological Law 

 of Evolution '). 



The transformation of the plant world is much less 

 than is generally supposed. It is true that we read in 

 all tuition books that the Coal flora, the New Ked Sand- 

 stone flora, and others, are fundamentally different from 

 each other and from that of the present day. In the 

 wall cartoons of Potonie this is shown in the clearest 

 way. These pictures show exactly the flora actually 

 found in the formations concerned, but as regards the 

 extent of the transformation established in single 

 definite groups a mere comparison between two or 

 more such ' landscapes 9 can teach us very little. 



This is because, first of all, in most cases it is only 

 parts of the flora concerned which are shown for 

 instance, moor plants : consequently moor should be 

 compared with moor. Furthermore, the climate at 

 the time concerned must be considered : the tropical 

 flora of the Coal era has its descendants mostly in the 

 tropics. Finally it must not be forgotten that plant 

 groups can die out and become extinct and, indeed, 



