THE MALE FERN DRTOPTERIS FILIX-MAS 



from Dr von. Tavel in 1939 spore samples of seven of his Swiss varieties and forms. 

 These were var. insubrica, var. disjuncta, var. ursina, var. ursina f aurea, var. tenuis, 'var. 

 tenuis nigricans', var. robusta, 'var. punctata'. AU of these were apogamous, and apogamy 

 had previously been recorded by Dopp (1939) in some plants from Germany. 



It would be a matter of considerable interest to know if sexual forms of this species 

 exist, but from their obvious scarcity the suspicion is aroused that they do not. If this 

 were known with certainty to be the case, a very interesting problem would be raised 

 as to the possible origin of these plants. Apart from undoubted hybrids with Filix-mas 

 (and perhaps with D. abbreviata), which will be referred to below (see also Chapter 11), 

 the morphological characteristics of D. Borreri concern a number of organs and both 

 morphological generations. A simple mutant origin of all these characters at once seems 

 somewhat improbable. An alternative explanation might be that both apogamy and 

 morphological characters were produced simultaneously by an act of hybridization, 

 the incidence of apogamy making the hybrid stable from the outset without other 

 cytological change (for further discussion of this, see Chapter 11). 



Be that as it may, it is certain that some cytological changes have taken place 

 subsequently. Within the D. Borreri complex a whole range of chromosome numbers, 

 in polyploid series, can be found. In the Swiss material var, disjuncta and 'var. punctata' 

 were diploid and the remainder triploid. In Great Britain the majority of plants are 

 triploid (Figs. 46, 48) but extensive local diploid populations have been met with in 

 Ireland, Wales and the Lake District. Diploids and triploids are so much alike that 

 I have not succeeded in detecting any constant morphological differences that will serve 

 for their identification in the field in a new locality, except perhaps spore size which is 

 greater in the triploid than in the diploid, and it is significant that when pressed fronds 

 of British plants were submitted to Dr von Tavel, a diploid from north Wales was 

 identified as var. insubrica which in Switzerland was triploid, with only the remark that 

 the sori in the Welsh specimen were smaller. 



Without at the moment discussing the possible origin of polyploidy within D. Borreri 

 which will more easily be dealt with at a later stage (cf Chapter 11), an extension of 

 the polyploid series by subsequent hybridization with D. Filix-mas can nevertheless 

 be detected. An artificially produced hybrid between D. Filix-mas as female parent 

 and a horticultural strain of diploid D. Borreri with forked leaves, was described by Dopp 

 in 1939, the hybrid being identified as such with complete certainty by having the 

 forked fronds and apogamous reproduction derived from its male parent, but combined 

 with the tetraploid and not the diploid chromosome number. The output of 'good' 

 spores was also much reduced. I have not myself repeated Dopp's experiment for the 

 reasons explained in the Preface, but it is not unusual to find individual specimens of 

 closely comparable type where populations of the two species are growing together in 

 the wild state. Such plants will show the wealth of ramenta and the dark spot on the 

 pinna rachises characteristic of D. Borreri combined with the pinna shape and some 

 other characteristics of Z). Filix-mas. The spore output is low, but such 'good' spores 

 as may be formed, which are always very large, give rise to apogamously reproducing 

 prothalli. In two cases found by myself the chromosome number of such plants 

 proved to be tetraploid, as in Dopp's hybrid, but two other cases picked out on their 



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