202 



CYTOGENETIC STUDIES IN DRYOPTERIS SPINULOSA : I 



Fig. 7. Explanatory diagram of Plate 16, fig. (c) showing meiosis in the triploid hybrid D. dilatata (4n) X 

 " D, dilatata " (2n-Scotland). n = 39 pairs + 45 singles (X 1500). 



(7) D. dilatata (4n) X " D. dilatata" (2n-Madeira) - A frond from a 3 year old 

 hybrid plant in which the female parent was diploid is illustrated by Fig. 3 (b). Com- 

 parison of this with Fig. 2 (b) shows clearly the morphological differences found in 

 triploid " D. dilatata " when the European or Madeiran diploid forms are used. Eleven 

 analyses of meiotic chromosome pairing in one cross and four analyses from the reciprocal 

 cross have been made. In all cells except one the number of bivalents ranges from 34 to 

 37 together with the corresponding 55 to 49 univalents; nine cells show 36 pairs and 51 

 singles. In one cell, however, as illustrated by Plate 16, fig. (d) and explanatory Fig. 8 

 one quadrivalent and one trivalent were found. One or two cells in anaphase have also 

 suggested multivalent formation but the percentage is small. Small segmental inter- 

 changes between chromosomes otherwise non-homologous are probably the cause of 

 multivalents in this case. 



(8) " D. dilatata " (2n-Scotland) X D. spinulosa- Fig. 2 (c) shows the outline of a 

 frond from a hybrid plant when 18 months old. Intermediate characters between the 

 parents such as pinnation, non-prostrate rhizome and two-coloured scales are evident 

 in living specimens. Reciprocal crosses have been made and, in all, eight cells analysed 

 during meiosis; 38 paired and 47 single chromosomes can be seen as in Plate 16, fig. (e) 

 and explained by Fig. 9. Variations of zb one bivalent have been found in three of the 

 plates examined. 



(9) " D. dilatata" (2n-Madeira) X D. spinulosa - AgdLin. reciprocal crosses have 

 been made and Fig. 3 (c) shows a frond from a hybrid, when 18 months old. Cytological 

 investigation of meiosis has shown 35 bivalents and 53 univalents in 7 analysed cells and 

 34 bivalents with 55 univalents in two other cells. An example of the former arrangement 

 can be seen on Plate 16, fig. (f ) and explanatory Fig. 10. 



(10) D. cristata X " D. dilatata" (2n) - No hybrids have been formed when 

 attempting to cross D. cristata with either of the diploid forms of D. dilatata from Scotland 



