194 CYTOGENETIC STUDIES IN DRYOPTERIS SPINULOSA : I 



D. cristata was first named by Linnaeus in 1753 as Polypodium cristatum. D. 

 spinulosa was not recognised as a separate species until described as Polypodium spinu- 

 losum by Miilier in 1767 and D. dilatata was not considered distinct from P. spinulosiun until 

 1795 when it was named Polypodium dilatatum by Hoffmann. 



Since these dates of separate recognition the generic conception has changed and 

 the plants have been placed under Aspidium, Nephrodium, Lastrea, Thelypteris and Dry- 

 opteris. It is more significant, however, that some authors have referred to the three 

 species merely as subspecies or even varieties of a single species (Newman, 1844, 1865 ; 

 Druery, 1912). The specific epithet dilatata has been replaced in the new Flora of the 

 British Isles (Warburg, 1952) by austriaca, following the continental nomenclature, and 

 D. cristata, D. spinulosa and D. austriaca (Jacq.) Woynar, 1915, are recognised as distinct 

 species. 



The use of the name D. austriaca raises problems of its own, however. Christensen 

 (1913-16) states that " D. austriaca = D. spinulosa " and this was at a time when Christen- 

 sen considered D. spinulosa and D. dilatata as separate species. The original name 

 Polypodium austriacum was given to a fern collected by Jacquin (1764) but the type 

 specimen is unavailable, even if one exists. Herbarium sheets from Jacquin' s herbarium 

 at the British Museum and labelled "P. austriacum", but not by Jacquin, are a mixed 

 collection of genuine D. spinulosa and D. dilatata. Without returning to the type locality, 

 a decision regarding the identity of D. austriaca cannot be reached arid for this reason 

 the writer prefers the retention of the name D. dilatata. 



(2) Materials 



A number of collectors have helped to supply the material for the investigation, all 

 of which has been checked for identification and c3/tological behaviour. Representative 

 plants of all the specimens collected (except one) have been maintained in culture and 

 herbarium specimens kept by the writer. A duplicate set of herbarium specimens is to 

 be deposited with the British Museum (Natural History), London. 



The material of D. cristata was collected and supplied originally from Surrey, England 

 by its discoverer in that locality (Payne, 1939) and is now in cultivation at the Royal 

 Botanic Gardens, Kew. From this specimen a number of plants have been raised and 

 are now in cultivation at Liverpool. D. spinulosa has been sampled from England, France, 

 Germany and Sweden. D. dilatata is known to include two cytological forms, one diploid 

 and the other tetraploid (Manton, 1950). The tetraploid has been collected from France, 

 Germany, Sweden, Ireland and many localities in England, and the diploid from Norway, 

 Sweden, Switzerland, Scotland and also the island of Madeira (consideration of this 

 plant is included here although it is from outside Europe). 



Only one plant of the hybrid D. X uliginosa has been available owing to its relative 

 rarity; this is maintained in cultivation at Leeds and was used also by Manton (1950) 

 for cytological study. A number of specimens of the h3'brid between D. spinulosa and 

 D. dilatata have been collected from two Yorkshire (England) localities and a single 

 specimen from Ireland, the latter having been found by Dr. R. L. Praeger. 



(3) Methods 



Prothallial cultures were grown in 3 in. pots containing a sterilised compost com- 

 prising peat, loam and sand in the ratio of 3 : 2 : 1 respectively. The pots were protected 

 from stray spores by clock glass covers and watered only from below, thus preventing 

 access to free surface water and minimising the chances of fertilisation within parent 

 cultures. The young prothalli could be maintained in a more juvenile state for a longer 

 period if grown at temperatures of 70° to 80°F; in these conditions they were found to 



