THREE SPECIAL CASES OF FERN HYBRIDS: 



make and a number of examples were attested as such by a triploid chromosome count. 

 In appearance they resemble pure P. aculeatum so closely that their hybrid nature might 

 escape detection in a herbarium specimen unless the spores were examined and seen 

 to be abortive. Meiosis is, however, characteristic. The first sporangia were produced 

 in 1947, and the plants were fully fertile in 1948. Figs. 161 and 162 show a sample cell. 

 As expected, pairing closely resembles that of the other triploid. In the figured cell 

 there appear to be 41 pairs and 40 identifiable univalents. Since n — /\.i this is sufficiently 

 close to expectation to confirm the suggested close relationship of P. angulare with 

 P. aculeatum. 



If this conclusion is correct it ought therefore to be possible to resynthesize P. aculeatum 

 by crossing P. angulare with P. Lonchitis followed by colchicine treatment. It is hoped 



Fig. 161. Meiosis in the triploid hybrid between Polystichum aculeatum (L.) Roth and P. angulare (Kitaib.) 

 Presl (Fig. 160), permanent acetocarmine. x 1500. For explanatory diagram see Fig. 162. 



that this will indeed be done, and that the resulting plant will in fact resemble 

 P. aculeatum. If it does not it would be necessary to look at other diploid species of the genus 

 sufficiently close to the two in question to be likely to have chromosomes homologous 

 with these. To pursue this matter further at the moment, however, is impossible, since 

 even the synthesis from known parents would take at least 5 years to carry out and test. 

 The importance of P. illyricum in a general inquiry such as this is, however, obvious. 

 It has provided a clue to the genesis of yet one more polyploid hybrid species, and by 

 doing so has completed the analysis of a common British plant in terms not of suspected 

 relationship or certain affinity on one side only, as in the case of the Male Fern and 

 Woodsia, but with very strong probability indeed with respect to both the parents of the 

 hybrid species. This degree of completeness is a very welcome addition to the analyses 

 already discussed in this and previous chapters. 



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