APOGAMOUS FERNS. EVOLUTION OF THE SEPARATE SPECIES 



Pteris cretica L. is widespread and abundant in the tropics of the Old World, although, 

 somewhat surprisingly, it has a number of outlying stations in Europe and, owing to its 

 ease of cultivation and tolerance of the dry air of dweUing houses, it is an even greater 

 favourite as an ornamental plant of commerce (cf. Fig. 172) than is Cyrtomium. Most 

 of the considerable range of horticultural varieties have arisen in cultivation, and it is 

 doubtful whether the genuine wild species is present at all in greenhouses at the present 



Fig. 173, Meiosis in Pteris cretica L. from sections stained in haematoxylin and counter-stained with 

 Bismark brown to show unusual excellence of fixation, a. Diploid P. cretica first meiotic metaphase 

 in an eight-celled sporangium, x 1000. b. The same, anaphase, c. The same in a sixteen-celled 

 sporangium. Note smaller cells and lagging chromosomes at both metaphase and anaphase. 

 d. Triploid Pteris cretica var. albolineata. Diakinesis in an eight-celled sporangium, x 750. 



time. An exception is, perhaps, var. albolineata, for this was described by Hooker as a 

 wild variety with variegated fronds native to the Far East, and comparison which 

 I have been able to make with a reputedly wild specimen from Ceylon supplied by 

 Peradenya Botanic Gardens showed no detectable difference of any kind between it 

 and examples of the variety already in cultivation in England. It has, however, long 

 been known (cf de Litardiere, 1920) that the native European species has fewer 

 chromosomes than the morphologically normal 'var. major' of commerce. The numbers 

 given by de Litardiere were 2/2 = 60 and 120 respectively, the low number being 



173 



