SYNTHETIC CHARACTER OF PALEO-ECOLOGY 371 



as the middleman between the habitat and the animal life. It is an effect 

 to the one and a cause to the other. It is obvious that the total relation 

 is far more complex than this, since factors do act directly on animals as 

 well; but it must be granted that the study of plants and plant communi- 

 ties does enable us to look in both directions — that is, back to the physical 

 factors of the habitat and forward to tlie animal responses. In addition 

 to this basic causal sequence is the resulting reaction sequence in which 

 animals react on plants and plants on soil and climate, to say nothing of 

 the direct action and reaction between liabitat and animals. In emplia- 

 siziug the primary value of sequences, there is no need to assume that 

 plants are the most imjDortant part of paleo-ecology because of their 

 strategic medial position. They do, however, afford the best points for 

 entering this vast field. 



Methods or emploiting previous ecological Eesults 



The methods by which the ecological results of today can be carried 

 back into the past have been briefly discussed in "Plant Succession" and 

 it wdll suffice to pass them in review here. For the most part these are 

 methods with Avhich the paleontologist is already familiar, since they 

 have to do primarily with the translation of facts from the present to the 

 past. The foremost is the method of causal sequence, already mentioned, 

 with its basic relation of habitat, plant, and animal. This is well illus- 

 trated by the occurrence of Stipa in the Miocene of Florissant, which 

 indicates not merely the existence of prairie, but also, of course, a grass- 

 land climate and a grazing population. A similar but even more funda- 

 mental sequence begins with deformation and passes through grada- 

 tion, climate, and vegetation to exhibit its final effects in the fauna. 

 The method of phylogeny which has been the most serviceable of taxo- 

 nomic tools is likewise of great value in the reconstruction of the life 

 forms and communities of the past. It shares with the method of suc- 

 cession the credit of permitting us to give more and more detail to the 

 bold outlines of past vegetations and vegetation movements. The method 

 of succession is based on the great strides made by the developmental 

 study of vegetation during the last twenty years. When successional 

 studies become the rule in zoo-ecology as well, there will seem to be no 

 limit to the increasing perfection of detail in jDicturing the rise and fall 

 of past populations and comnmnities. In the case of vegetation, this 

 method has already gojie so far as to l)ring conviction that all the essen- 

 tial features of successional processes and climax communities as seen 

 today already existed in the past. As indispensable corollaries of the 

 methods of phylogen}' and succession arc inferences from distribution in 



