s. Walker 



203 



4.. 



Fig. 8. Explanatory diagram of Plate 16, fig. (d) showing meiosis in the triploid hybrid D. dilatata (4n) 

 X " D. dilatata " (2n-Madeira). n = 1 quadrivalent + 1 trivalent + 34 pairs + 48 singles (X 1500). 



Fig. 9. Explanatory diagram of Plate 16, fig. (e) showing meiosis in the triploid hybrid D. spinulosa X " D. 

 dilatata " (2n-Scotland). n = 38 pairs + 47 singles (X 1500). 



cr Madeira. Two young plants which did develop were found to be normal D. cristata 

 which had been used as the female parent and probably selfed at the time of attempted 

 hybridisation. 



Attempts to synthesise any hybrid utilising D. cristata as one parent have not been 

 successful. The prothallial cultures of this species have never produced sex organs in 

 quantity; the numbers of swimming spermatozoids have been relatively small and mature 

 archegonia few at any one time. This may be attributed to the present cultural conditions 



