86 



MORPHOLOGY OF ANGIOSPERMS 



the nucleus nearer the micropyle, as shown for Trillium in 

 Fig. 28. Hence the megaspore at the chalazal end of a row- 

 is "formed a little earlier than the one at the micropylar end. 



A 



B 



Fig. 33. — C'rucianella macrostachija. A, four-nucleate embryo-sac and three disintegra- 

 ting megaspores ; the four megaspores of this axial row not separated by cell-walls. 

 H, axial row of four megaspores which are not separated by cell-walls ; each mega- 

 spore has germinated and is in the binucleate stage. C, an embryo-sac (with two 

 nuclei) and four sets of megaspores ; the megaspores of one set germinating. — After 

 Lloyd." 6 



A still more important reason for the selection of the chalazal 

 megaspore is doubtless its more immediate relation to the nutri- 

 tive supplies coming through the base of the ovule, a fact which 

 may also account for the earlier mitosis at the chalazal end of 

 the row. 



In case there is more than one mother-cell, two or more 

 megaspores may begin the development of embryo-sacs, which 

 may even attain the fertilization stage, but in almost every ease 

 one embryo-sac prevails over the others. Among the Monocoty- 

 ledons two embryo-sacs are reported as sometimes occurring in 

 Lilium candidum (Bernard 84 ); and in Agraphis (Yesque, 4 

 Guignard 12 ) and Uvularia (Vesque 4 ), as referred to above, 

 all of the two or three megaspores of the single row develop 

 embryo-sacs to the four-nucleate stage. Among the Archichla- 

 mydeae, five to eight sacs begin to develop in Loranthus 



