THE FEMALE GAMETOPHYTE 



107 



micropylar end. The 4 mega spore nuclei are usually arranged tet- 

 rahedrally, but in the embryo sacs of the pear-shaped type one 

 nucleus projects rather conspicuously towards the upper papillate 



Fig. 



I K L 



69. Development of embryo sac in Peperomia pellucida. 



A, megaspore 



mother cell. B, two-nucleate stage. C, four-nucleate stage. D,E, eight-nucleate 

 stage as seen in spherical and pear-shaped tj^pes of embryo sacs respectively. 

 F,G, 16-nucleate stage. H, mature embryo sac of spherical type, showing a single 

 synergid, six lateral cells, and eight polar nuclei (all nuclei of sac are not seen in 

 this section). 7, same, showing one lateral cell in close proximity to egg and there- 

 fore simulating a second synergid. J-M, successive sections through a pear-shaped 

 embryo sac, showing a three-celled egg apparatus. (After Fagerlind, 1939a.) 



end. In the next stage, the 8 nuclei are either distributed more 

 or less symmetrically around the periphery of the embryo sac (Fig. 

 69D), or 2 nuclei may lie somewhat closer to each other at its upper 

 end (Fig. 692?) . The fourth and the last division now gives rise to 



