1908] COULTER— MEGASPORES AND EMBRYO SACS 363 



In the older papers many records of "three megaspores," "two 

 mcgaspores/' and "no megaspores"- appear, which cither must be due 

 to incomplete investigation or represent such an elimination of 

 divisions as is shown by Lilium and Cypripedium. 



What has been regarded as the most striking exception to the usual 

 structure of the angiosperm embryo sac is the case of Peperomia 

 pellucida, described by Campbell^ and Johnson.^ In this sac 

 sixteen nuclei appear before fertilization ; that is, there appears to be 

 one more division than usual. Lately Johnson^ has described a 

 similar condition in the Jamaican Peperomia hispidula, in which there 

 are also eight-nucleate sacs. 



Fortunately, in the case of Peperomia we know that the mother 

 cell does not divide to form walled megaspores, so that the probable 

 mterpretation of the situation is evident. Four mcgasporc nuclei 

 are formed, all of which are probably involved in forming the female 

 gametophyte. By two successive divisions each of these gives rise to 

 four nuclei, and the result is sixteen nuclei. It follows that the ordinary 

 number of successive divisions has been reduced from five to four; 

 and that if Peperomia had suffered no reduction, there would have 

 been thirty-tw^o nuclei in the embryo sac. In number of dinsions, 

 therefore, Peperomia lies between the ordinary angiosperms on the 

 one side, and Lilium and Cypripedium on the other. This condition 

 should be regarded as advanced in the direction of the elimination of 

 divisions, rather than primitive. If an embryo sac derived from a 

 single megasporc should contain sixteen nuclei, it could be regarded 

 as relatively primitive; but the sac of Peperomia could contain thirty- 

 two nuclei and only be normal. Peperomia hispidula is interesting 

 in developing eight-nucleate sacs in addition to the sixteen-nucleate 

 ones, which perhaps puts it upon a level of reduction with Lilium. It 

 may have some bearing on the situation to note also that Johnson in 

 Ills account of this species described the first four nuclei of the sac as 

 "arranged in a perfect tetrad," which would be quite natural for 



n 



= Campbell, Douglas H., Die Entwicklung des Embryosackes von Peperomia 

 pellucida Kunth. Ber. Deutsch. Bot. Gesells. 17:452-456. pl- 3^- 1899- 



3 Johnson, D. S., On the endosperm and embryo of Peperomin pellucida. Box. 



Gazette 30:1-11. ph. 28, 29, 1900. 



OHNSON 



ilim 



Johns Hopkins Univ. Circ. 1907:19-21. p!s. 5, 6. 



