4 INTRODUCTION TO VOLUME III 



writers, are by no means uniform. It is believed that the wider field of 

 criteria here adopted may serve as a reliable guide in deciding some critical 

 questions upon which authorities have disagreed. It is not in the spirit of 

 the iconoclast that the systematic grouping of Leptosporangiate Ferns has 

 been approached : but rather with a feeling of the deep respect that is due 

 to the pioneers of classification, and with the highest appreciation of the . 

 work which they have carried through. 



The author does not profess to a critical knowledge of the species and 

 varieties of Ferns at large. Those who are happy in possessing it may find 

 themselves at variance here and there with the conclusions as stated. He 

 would ask them, wherever this is so, to try to reconsider the position along 

 the lines of argument here advanced : and it may be that, with a slightly 

 modified valuation of the relative importance of certain characters as 

 compared with others, the suggested groupings may be found more worthy 

 of consideration than they appeared to them at first to be. 



It will be gathered from what is contained in these paragraphs that the 

 work does not purport to be one of precise systematic treatment, but rather 

 a morphological commentary upon the methods by which a natural grouping 

 may be approached. From time to time statements will, however, be made 

 of such tentative conclusions, general rather than specific, as seem to follow 

 from the application of a method wider in its field than could have been 

 available to the earlier writers. Perhaps these may aid the studies of 

 Systematists of later date. 



It is a matter for regret that the detailed knowledge of the gametophyte 

 of Leptosporangiate Ferns is still very deficient. Its features are certainly 

 more uniform, and offer less opportunity for comparative use than is the 

 case in the more primitive Ferns. Nevertheless it may be that more 

 extensive and detailed observation of them than has yet been carried out 

 may in the future provide a fresh area of fact yielding material assistance 

 towards phyletic conclusions. Here, however, the weight of comparison 

 necessarily falls even more definitely upon the sporophyte than the avail- 

 able facts have allowed in regard to the Ferns of Mesozoic and Palaeozoic 

 types. 



In the naming of the species cited in these Volumes the Index Filicmn of 

 DrCarl Christensen has been followed : and the author desires to acknowledge 

 his profound indebtedness to the compiler of that most useful work. It is 

 generally recognised as standardising the confused nomenclature of Ferns, 

 while the tabular presentment of their classification in the earlier pages (l-Lix) 

 gives in a most convenient form a condensed statement of the groupings of 

 Diels. This should not be accepted as an expression of considered opinion 

 by the author of the Index, but as an historical document of the position at 

 the time when Engler and Prantl's Volume IV was published. 



