■"^="':i PLANT LIFE OP THE GLOBE. 439 



plete view of the classification warranted by the present knowledge of 

 plant life may be gained. 



7. GEOGNOSTICO-BOTANICAL VIEW OF THE PLANT LIFE OP THE 



GLOBE. 



We will now attempt to marshal in as convenient a form as possible 

 the principal facts which paleontology and modern botany afford, with 

 a view to examining their bearings upon the problem of classification 

 in general and upon those of descent and develoijment in particular. 

 In doing this we are compelled to depend upon the weight of evidence 

 furnished by the number of species alone, since it is impossible to take 

 account of the relative predominance of species, however great and 

 important the differences may be in this respect. The number of 

 species really marks the degree of variety or multiplicity, which cer- 

 tainly forms a rude index to the degree of abundance or prominence. 

 Where a number of types are compared this difference in their degree 

 of variety may fairly be assumed to apply to all alike, and the conclusions 

 thus drawn will be measurably accurate ; and in general this multiplicity 

 of varying forms under larger types may be taken in a manner to rep- 

 resent the relative exuberance or luxuriance of the type, and thus 

 roughly to indicate its relative predominance as a form of vegetation. 



In all attempts to argue from paleontology allowance must, of course, 

 be made for the imperfection of the geological record, and in no de- 

 partment is this imperfection greater than in that of plants. Yet it is 

 certainly remarkable how large a portion of the earth's surface has, 

 at one epoch or another, presented the conditions which have proved 

 favorable to the preservation of vegetable remains. Our surprise at 

 this is heightened when we contemplate the present state of the globe 

 upon which that condition seems scarcely to exist. We know that the 

 great land areas of our continents are wholly incapable of preserving 

 the leaves that annually fall upon them, and it is only in the quiet beds 

 of rivers that have reached their base level, or in their deltas, or else 

 in localities where tufa-laden spring water flows over vegetation, or 

 lastly, in our great swamps, that such a result is possible. This last 

 condition is believed to furnish the key to the solution of the problem 

 of most of the ancient vegetable deposits, but the limits of this paper 

 forbid me to enter into a discussion of this subject. 



The following table presents in a rough manner the history of the 

 introduction of plant life upon the globe as revealed by the remains 

 that have actually been discovered. It has been compiled from about 

 25,000 species slips which have been the product of nearly two years' 

 labor in cataloguing the literature of Paleobotany. Although this work 

 is by no means completed, still, it embraces nearly all the more recent 

 and more important works on the subject, and hence cannot fall far short 

 of affording a correct view of the present state of knowledge of the 

 fossil flora of the globe. 



