6o2 THE POPULAR SCIENCE MONTHLY 



In the groups of spore-bearing plants ordinarily found fossil, the 

 spores are not known to have developed any particular devices for their 

 wide dissemination, such as flotation in air, attachment to animals, etc. 

 They are produced in vast quantities, and depend upon a few reach- 

 ing situations favorable for successful germination. Their vitality is 

 also of apparently exceedingly limited duration, and it is doubtful if 

 they could long survive immersion in salt water. 



The bearing of the above digression is apparent. Given a fossil 

 flora made up of ferns or fern allies, exclusive of what are known to 

 belong to the cycadofilices, and when such flora is found in two or more 

 separated areas, we are justified, in my opinion, in arguing a practically 

 continuous land connection. They were incapable of crossing very wide 

 reaches of open water, particularly salt water. Fresh-water streams 

 have been to some extent avenues of distribution, but many fossil 

 floras — and living floras as well — are too widely spread to be explained 

 by this means. "When, as is usually the case, identical floras occupying 

 different areas are mixed floras, the bearing on the means of reaching 

 the various areas is more complicated. An example may better serve 

 to bring this out. Thus, the Jurassic flora is practically world-wide 

 in its distribution, ranging from Franz Josef Land, 82° N., to Louis 

 Philippe Land, 63° S. It is composed of ferns, fern-allies, cycads and 

 conifers, a large percentage being true ferns. The probability of a 

 close land connection argued on the basis of the true ferns, has already 

 been alluded to. The cycads — the Jurassic is called the age of cycads 

 — were abundant in individuals and numerous in forms. On the basis 

 of our knowledge of living types, it may be stated that cycad seeds 

 germinate immediately on falling from the cone without any necessary 

 resting period. They are not known to retain their vitality for a 

 longer period than three years, and usually but two years. They sink 

 promptly in fresh water and as the stony coat is easily penetrated by 

 water, they either germinate or rot at once. In salt water they will 

 probably sink and decay even more quickly. Therefore, the probability 

 of their being transported for any great distance over open water is 

 reduced to a minimum. The conifers of the Jurassic were reproduced 

 by seeds. They belong to types not known to enjoy any special means 

 for transportation, nor is it probable they could better withstand fresh- 

 or salt-water immersion than the cycads. All classes of vegetation 

 present in the Jurassic, therefore, argue for a practically continuous 

 land connection. 



In considering the bearing of any flora on the paleogeographic 

 problem the process is similar to that outlined above. That is, an 

 analysis of the composition of the flora, a study of the means of nat- 

 ural dissemination which includes duration of vitality, and finally a 

 judgment as to its probable means or avenues of transportation, in- 

 volving a land connection or otherwise. 



