ITS LIMITATIONS 229 



Cordaiteae, a type already very, perfect and specialised. We cannot then 

 draw from the data of Palaeobotany which we possess any indication of 

 the origin of these first Gymnosperms." This illustrates how hopeless it 

 must be, so long as earlier strata yield only indefinite remains or none at 

 all, to base upon stratigraphical evidence any consecutive story of the 

 rise of a Land-Flora : for on a comparative basis these Gymnosperms which 

 thus appear so early stand high in the scale of Vascular Plants. Other 

 examples might be quoted, but this will suffice to illustrate the deficiency 

 of .the record as regards prime origins. It has already been noted that 

 developmental detail is usually absent from fossils, and that many are 

 known only as impressions, without the possibility of minute structural 

 examination of their tissues under the microscope. These considerations 

 only show still further how scanty is the positive information from study 

 of the fossils which is available for elucidating the . early origin of the 

 sporophyte. 



There is also a converse line of information, which involves negative 

 evidence, based on the absence of certain types from strata where others 

 are present. It may be held that organisms which first appear in the 

 earlier strata are more primitive branches of the evolutionary tree than 

 those which appear only in the more recent strata. But the fact that the 

 record is, as we have seen, so very incomplete as regards the prime origins 

 of the leading phyla will at once strike the note of caution in use of 

 such negative arguments. Moreover, the probability of preservation of the 

 representatives of any group may depend greatly on the character of the 

 organisms in question : thus it need be no surprise that the small and 

 delicate Bryophytes are conspicuous by their absence from the earlier 

 records, while Algae are but rarely preserved. Again, the non-representation 

 of any group may depend in some measure on the position in which the 

 plants grew : thus the flora of uplands will be less likely to be preserved 

 than that of low-lying lands or swamps ; this argument has sometimes 

 been applied in explanation of the absence of Angiosperms till a relatively 

 late period. It is often possible to make out a plausible case from such 

 negative evidence : but its insecurity is obvious. To use it with effect 

 it must be supported by other considerations, such as argument from 

 comparison. Thus the' absence of evidence that Polypodiaceous Ferns 

 existed in Palaeozoic times, must be taken with the position which is 

 assigned to them on grounds of comparison among other Filicales; it 

 then becomes a very convincing argument as showing their later derivative 

 character, and the more so that Fern-types are among the best-preserved 

 of early fossils. On the other hand, the entire absence of well-authenticated 

 Ophioglossaceous remains from all the earlier formations only intensifies the 

 difficulty of the problem which surrounds these curious plants, and cannot in 

 itself be accepted as demonstrating that they are of relatively recent origin. 



These remarks are intended to indicate the limitations to which the use 

 of palaeophytological evidence must necessarily be subject. It is when these 



