Department of Botany, University of Leeds, Leeds LS2 9JT, UNITED KINGDOM.
The basic aim of this research project is to attempt to obtain information concerning the phyletic affinities between species by means of a study of chromosome pairing in synthesised hybrids. Any evidence obtained is supplemented by a consideration of the morphology, ecology and geographical distribution of the species concerned.
The main problem consisted of a cytogenetic investigation into the relationships of the four European Polystichum species, although this soon resolved into the two immediately accessible problems of the affinities and possible origin of the two tetraploids P. braunii (continuing the observations of Manton & Reichstein, 1961) and P. aeuleatum. Attempts were made to resynthesise the latter species from it s postulated parents (Manton, 1950).
Polystichum is a slow-growing fern and it was known that synthesised hybrids may need up to three years to produce sporangia. Because of the possibility that hybrids obtained might mature too slowly to yield results in the time available an additional investigation involving some Asplenium species was begun. In this genus many hybrids produce sporangia within a year of fertilisation, thus permitting a rapid extension of the hybridisation programme. This considerable advantage has converted a secondary investigation into the mutual affinities: of two European tetraploids (A. forisiense and A. macedonicum) into a major project, and the hybridisation programme was expanded to include a number of other European species at both diploid and tetraploid levels. Much new material was made available from the personal collections of Professor Eeichstein of Basel, who was also responsible for obtaining an important collection of living Polystichum species from Japan by arrangement with Professor H. Ito of Tokyo. Both investigations have therefore extended beyond the bounds first envisaged but since the work on Asplenium is more nearly complete it will be convenient to deal with it first in the account which follows.
Each genus is treated separately as a distinct section with the exception of the account of the methods used, which follows, and the General Discussion, which will be found at the end of the thesis.