S. WALKER 



101 



Fig. 6. Explanatory diagram of Plate 15, fig. (d) showing meiosis in the triploid hybrid ' ' D. dilatata " (Bavaria). 



n = 38 pairs + 47 singles (X 1500). 



been unsuccessful. The two species are ecologically separated in the wild and, so far, a 

 wild hybrid is unknown. 



(4) D. dilatata (4n) X " D. dilatata " (2n-Scotland) - A frond from a 3 years old 

 plant of this combination is illustrated by Fig. 2 (b). In this particular plant the tetraploid 

 had been used as the female parent. The morphology of the hybrid tends to be inter- 

 mediate between that of its parents but likeness with the diploid is most evident. Tetra- 

 ploids of different origin have been used with similar success and the reciprocal cross 

 has also been made. Six chromosome analyses of meiosis in one cross and eight of the 

 reciprocal show, in the majority of cases, 39 bivalents and 45 univalents. This can be 

 seen in the photographed cell, Plate 16, fig. (c) and explained by Fig. 7. In two cases 

 the number of bivalents formed was 38 and in another was 40. 



(5) D. dilatata (4n) X " D. dilatata " (2n-Norway) - Spores collected from a plant 

 in Trondheim, Norway were used as the source of the diploid in this hybrid. The original 

 diploid plant was not maintained in culture but was examined cytologically by M.uiton 

 (1950) and a herbarium specimen kept. Reciprocal crosses have been m ide. Altogether 

 nine cells have been analysed at meiosis, seven of which show 39 paired and 45 unpaired 

 chromosomes. The other two show 38 bivalents and 47 univalents. 



(6) D. dilatata (4n) X " D. dilatata " (2n-Switzerldnd) - Using the diploid as 

 female, 19 hybrids have, so far, been confirmed. The reciprocal cross has not been attempted. 

 Only three cells have been completely analysed for chromosome pairing and, as in the 

 previous hybrids involving European diploid and tetraploid forms of D. dilatata, 30 pairs 

 and 45 singles can be recognised. 



