SCOLOPENDRIUM HTBRIDUM, WOODSIA AND POLTSTICHUM ILLTRICUM 



The interpretation, of this series is fairly straightforward. The presence of the triploids 

 is in itself sufficient evidence for the correctness of the original diagnosis of the cross. 

 The presence of the others seems therefore necessarily to mean that this hybrid when first 

 formed is not completely sterile. There is no direct evidence of the nature of the 

 descendants which would be produced, but the behaviour of autotriploid Osmunda is a 

 helpful indication. If the expected proportion of balanced spores with the even poly- 

 ploid numbers can be formed, they would certainly be viable and the reversion to the 

 parental chromosome numbers would therefore not be surprising. That some signs of 

 hybridity still persist in such progeny would merely seem to imply that some extra 

 chromosomes belonging to one or other species are still present or that a measure of 

 gene exchange can occur between the chromosomes of the two species. 



b c 



Fig. 157. Meiosis in Polystichum illyricum Hahne and its parents, from sections, a. P. aculeatum (L.) Roth, 

 wild fixation, x 750. b. P. Lonchitis (L.) Roth, wild fixation, x 750. c. P. illyricum Hahne, 

 grown in cultivation, good fixation, x 1500. 



Be that as it may, an important taxonomic deduction follows from the study of 

 meiosis in the triploid plants. The evidence on this is presented in Figs. 157^, 158 and 

 159. Fig. 157^ shows meiosis in a triploid plant from the 1937 collection which had been 

 sent to England and grown on; exactly comparable results were also obtained in that 

 year from a hybrid plant fixed in the garden at Pont-de-Nant. Paired and unpaired 

 chromosomes are present in both in almost equal abundance, and the formation of 

 trivalents is so inconspicuous as to be negligible. More completely analysable evidence 

 is presented in Figs. 158 and 159 from acetocarmine preparations from one of the 1947 

 triploids which had been sent to England and fixed the following year. This does not 

 resemble autotriploid Osmunda, but again agrees very closely with the triploid hybrid 

 between Dryopteris Filix-mas and D. abbreviata. The conclusion which appears necessarily 

 to follow from this is that Polystichum aculeatum and P. Lonchitis are related in a way 

 comparable to Dryopteris Filix-mas and D. abbreviata, namely, that Polystichum aculeatum 

 is an allotetraploid and P. Lonchitis is one of its parents. 



153 



