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Fig. 169. Various examples of imperfect cleavage resulting from the abnormal premeiotic division 

 ( = developmental type 3, p. 166) from sections, x 1000. a. Dryopteris atrata (Wall.) Ching [Nephro- 

 dium hirtipes (Bl.) Hook. ) showing partial cleavage of one cell. b. The same in Dryopteris remota A.Br. 

 at early meiotic prophase, c. The same in Pteris cretica L. var. albolineata. A small cell has been 

 cut off from a large one, but both are now in an early state of meiosis. d. Dryopteris Borreri var. 

 polydactyla Wills, e. Tripolar meiotic spindle in Pteris cretica var. albolineata. f, g. Dryopteris Borreri 

 var. polydactyla Dadds. Two very unequal-sized meiotic metaphase plates in the same sporangium. 



167 



