204 



CYTOGENETIC STUDIES IN DRYOPTERIS SPINVLOSA : I 



3>m 



lift 



4 



Fig. 10. Explanatory diagram of Plate 16, fig. (f ) showing meiosis in the triploid hybrid D. spinulosa X 

 " D. dilatata " (2n-Madeira). n = 35 pairs — 53 singles (X 1500). 



which, though satisfactory^ for other species, may have to be varied for a species like 

 D. cristata Vvhich normally inhabits acid bogs and swampy places. The need for preventing 

 access to free water within cultures may be disadvantageous for the normal growth and 

 sex organ development in prothalli of D. cristata. 



(6) Discussion 



Hybridisation within the D. spinulosa complex and the corresponding c\-cological 

 evidence given above is represented by Fig. 11. Reciprocal hybrids ha\-e been studied 

 in all the synthesised lines but no cvtological differences found. Chromosome counts 

 of the species and wild or synthesised hybrids so far investigated are summarised in 

 Table 2. 



In the genus Dryopteris the basic haploid chromosome number is x = 41 (Manton, 

 1950). The presence of 39 bivalents during meiosis in D. :< uliginosa and of 33 in the 

 hybrid D. dilatata X spinulosa is therefore highly significant since these numbers are 

 not far removed from 41. Either autoploidy exists in one or more of the tetraploid 

 species D. cristata, D. spinulosa and D. dilatata, in which case the bivalents could be 

 formed from the gametic chromosome set of the autoploid parent, or there is evidence 

 of alloploidy with common ancestral diploids, one between D. cristata and D. spinulosa 

 and another between D. spinulosa and D. dilatata. 



Not one of the three parent tetraploids exhibit multivalent formation during meiosis, 

 which would indicate duplicated sets of chromosomes common to autoploids, but this 

 ability may have been lost and yet the tendency for homologous pairing to occur in the 



