S. WALKER 



199 



0 

 0 



Fig. 5. Explanatory diagram of Plate 15, fig. (c) showing meiosis in the tetraploid 

 hybrid D. dilatata X D. spinulosa. n = 33 pairs + 98 singles (X 1500). 



(B) Synthesised hybrids 



The programme of hybridisation is conveniently summarised by Table 1, in which 

 is indicated the number of attempts made at any one hybrid combination and the relative 

 amounts of success achieved. Further information is given below. 



(1) D. cristata X D. spinulosa - This attempt to synthesise D. X uliginosa has so 

 far been unsuccessful but more trials are being made. 



(2) D. dilatata X D. spinulosa (4n) - Using D. spinulosa from France as the female 

 and a British D. dilatata as male, it is probable that this wild hybrid has been synthesised; 

 cytological proof, however, is wanting. Two plants out of four potential hybrids were 

 normal D. spinulosa. The other two plants, however, exhibit glands on the rhachis and 

 rhacheolae and possess an almost erect rhizome ; these are now 3 years old but have never 

 developed beyond a juvenile stage with fronds of 2 in. to 3 in. high. A reason for this 

 lack of development is not evident. They have not produced fertile fronds and an investi- 

 gation of the somatic chromosome number would not give confirmation of hybridity 

 since both parents are tetraploid and the hybrid would be also. 



(3) D. cristata X D. dilatata (4n) - The few attempts to cross these species have 



