THE GENUS DRYOPTERIS IN BRITAIN 



The chromosomes of the Beech Fern {Phegopteris) are shown in some detail in Figs. 69- 

 71. In Fig. 71/meiosis is seen in a section, and the somewhat smaller size of the 

 chromosomes than in the species previously examined may be seen. The chromosome 

 number in the metaphase plate shown is of the order of 90 pairs, and this number can 



:• ••:r?> 







Fig. 69. Meiosis in the Beech Fern {Phegopteris). Permanent acetocarmine preparations, a, b. From 

 a British specimen, two cells in the same preparation, x 500. For explanatory diagram of a see 

 Fig. 70. c. A Scandinavian specimen from Storlien, Jamtland, Sweden, showing 90 chromo- 

 some pairs with exceptional clarity. 



be seen again in the squash preparations of Fig. 69, with one explanatory diagram in 

 Fig. 70 fl. The large cell of Fig. 69^ is a giant mother cell from the same sorus as Fig. 69 a 

 showing twice this number, an occurrence which will be discussed in greater detail in 

 Chapter 9. 



A section through a sorus of the Beech Fern, however, shows at once that the majority 

 of the sporangia have only 8 spore mother cells, instead of the customary 16, a condition 



82 



