THE GENUS DRTOPTERIS IN BRITAIN 



species {D. dilatata, D. spinulosa and D. cristata), in British and in continental specimens, 

 have a regular meiotic process and identical chromosome numbers which are n = 82 

 for the reduced number and 2^2=164 for the sporophytic somatic tissues. Sample 

 photographs to illustrate these facts will be found in Figs. 53, 55, 56 and 71, of which Figs. 

 53 c and 55 give the unreduced number for D. spinulosa, Figs. 53^ and 56 show an aceto- 

 carmine preparation of the British D. cristata, and Fig. 53/ shows meiosis in D. dilatata, 

 so perfectly that a diagram is not required. A view of D. dilatata in a section will be 

 found in Fig. 7 1 c. 



With regard to the hybrids, Fig. 57^ shows two spore mother cells from the hybrid 

 between D. dilatata and D. spinulosa at the first meiotic division in side view. The large 

 number of lagging unpaired chromosomes makes a striking contrast with the neat 



% 





,^^ 



.1. 





'^ '/ 



Fig. 57. Meiosis in Dryopteris spinulosa hybrids from sections, x 1000. 

 a, D. uliginosa; b, D. spinulosa x D. dilatata, wild hybrid. 



appearance of the parent species (Fig. 71c), and is sufficient confirmation of hybridity. 

 Since this particular hybrid is by no means rare, having been described from time to 

 time from many European countries and, in my experience, being not difficult to find 

 in Great Britain (I have examined specimens from England, Scotland and Ireland), 

 it may perhaps be of interest to field botanists to append a brief description of it. 



The hybrid between D. spinulosa and D. dilatata is met with not uncommonly in 

 mixed populations of the two parent species such as may occur, characteristically, where 

 an old and previously swampy D. spinulosa habitat is beginning to dry out. The hybrid 

 (Fig. 54c) shows a mixture of the characters of the two parents very clearly. It has the 

 semi-erect rhizome and dark coloured scales of Z). dilatata, but a relatively narrow frond 

 with the bottom pinna shorter than the one above it as in D. spinulosa. It will often show 

 hybrid vigour by growing to a very great size, and the profuse stoloniferous branching 

 of the stock will, in an old plant, cause it to lack the neat shuttlecock-like form of its 

 parents and to present instead a rather shapeless but compact jumble of fronds. The 



70 



