THE GENUS DRYOPTERIS IN BRITAIN 



sexual life history. The chromosomes agree with those of Phegopteris in their small 

 size, a fact which is demonstrated by comparing Fig. 7 1 d from a section of the Oak Fern 

 with other photographs on this page. The number, however, is different. Owing to the 



*■ V 



tCLyASgig'. 



d e f 



Fig. 71. Cytology of some species o{ Dryopteris in the wide sense seen in sections, x 1000. a. Meiosis 

 in D. Oreopteris (Ehrh.) Max. ti = 34. For further details see Figs. 65 and 66. b. Meiosis in D. aemula 

 (Ait.) O. Kuntze. n = ^i. For further details see Figs. 53a and 51. c. Meiosis in D. dilatata 

 (Hoffm.) A.Gray. n = 82. For further details see Fig. 53/. d. Meiosis 'miheOakYern{Gymnocarpium). 

 n = 80. For further details see Figs. 72 and 73. Note small size of the chromosomes, e. Mitosis in a 

 root of the Beech Fern (P/i^^o/)/mi). 2^ = 90. For explanatory diagram see Fig. 70^. f. Meiosis in 

 the Beech Fern {Phegopteris) with the same number of chromosome pairs as single chromosomes in 

 the root. For explanation see text. 



small size of the chromosome it has proved unusually difficult to determine their number 

 with absolute accuracy. In both species n is of the order of 80, and in the Oak Fern it 

 appears to be exactly this number (Figs. 72c, 73). It therefore seems possible that these 

 two species when better known may prove not to be identical with other European 



84 



