20 THE EVOLUTION OF PLANTS 



importance as historical documents, they are 

 not unworthy to be compared with the animal 

 record. If in some respects the botanist is less 

 fortunate than his zoological colleague, in others 

 he has the advantage. Though there is nothing 

 in plants quite like the skeleton, internal or ex- 

 ternal, of animals, so well adapted for preserva- 

 tion and so valuable as evidence, yet in knowl- 

 edge of outward form and anatomical structure 

 the fossil-botanist has the best of it. Besides the 

 impressions and casts of the stems, leaves, etc., 

 which are the best known kinds of plant-fossils, 

 we have in certain formations the still more 

 valuable petrified specimens, in which the mineral 

 substance, originally hi solution, has so thor- 

 oughly permeated the tissues as to preserve 

 their minute structure. We are thus able, for 

 example, to study by means of thin sections 

 the microscopic anatomy of many plants of the 

 Coal Measures, with almost the same accuracy 

 as if our specimens had just been gathered in 

 the garden, instead of having lain buried in the 

 earth for some millions of years. 



We cannot always expect to get evidence as 

 good as this, and every one knows that the fossil 

 record is imperfect; the surprising thing is 

 that it tells us so much. The subject of the 

 Evolution of Plants will be treated in this book 

 with constant reference to the fossil evidence. 



