CONCLUSIONS 



preferences the imprint of the most recent geological event which has engulfed this area, 

 namely a repeated succession of glacial and interglacial periods. 



If this is even partially true we are forced to the conclusion that, in the statistical 

 attributes of their cytology, the British ferns are not a representative sample of the ferns 

 of the world but that in details they are typical only of the vegetation of Europe in this 

 particular age and latitude. 



This need not, however, embarrass us unduly, for the microphyllous groups and 

 therefore the Pteridophyta as a whole can scarcely be subjected to statistical treatment 

 on our present limited knowledge, and discussion of them must therefore be confined to 

 those qualitative features which even a small or imperfect sample displays quite clearly. 

 Leaving this digression on the British ferns aside, we may therefore now proceed to 

 a more general discussion of the larger group of which the Filicales, though a part, are 

 only one among many. Lest, however, the reader should at this point expect the 

 impossible and look for a general discussion of all the varied aspects of a complex and 

 rapidly growing subject in a manner proper only to our imaginary historian of Chapter i , 

 it may be well to recall the rather limited terms of reference defined at the beginning of 

 Chapter 2 and within which the inquiry has been conducted. At the present stage it 

 would hinder and not help us to attempt to equate the results arrived at with all the 

 current views on general evolutionary topics which have been voiced from time to time 

 by students of other groups of plants or of animals. The remainder of this chapter will 

 therefore contain only a summary discussion of the facts presented in the book itself 

 and of the conclusions directly arising from them. The further evaluation of these, and 

 in particular their assimilation into the general body of knowledge which is mainly 

 based on the Flowering Plants, although it must eventually be attempted, would require 

 far more than the end of a chapter and may fittingly be left to the future. 



The first general conclusion from the work as a whole is perhaps the justification of the 

 method. Cytogenetics when applied with care and with modern techniques is at least 

 as informative in the Pteridophyta as in any other group of plants, and it is quite 

 certain that important new light will be shed on many hitherto insoluble problems of 

 taxonomy and of phylogeny when further work has been done. It may, however, be 

 well to warn a beginner yet once more against over-confidence and the hope of quick 

 results. The problems are legion and may be pursued in almost any country, but they 

 cannot be solved quickly, and unhmited care must be urged upon any would-be 

 investigator in the verification of specimens, in the recording of their places of origin 

 and in the full authentication of cytological observations, or, in a group as difficult as 

 this is technically, great harm may be done by the perpetuation of the types of error 

 which have dogged investigators with very few exceptions in the past and which once 

 recorded in print may be very hard to eradicate. 



A second conclusion is that the Pteridophyta as a whole while employing many of 

 the same evolutionary mechanisms as those of the Flowering Plants, have in some 

 respects proceeded further than the Flowering Plants, as their longer history had led 

 us to expect. The very high chromosome numbers recorded in every major group are 

 likely in themselves to be a sign of antiquity, though the continued presence, even in 

 the most ancient groups, of some genera and species with low numbers seems to 



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