AND THE Embryo-sac in Bignoxia venusta 101 



Divisions in the Formations of the axial Row of the 



nucellus 



Bignonia has not proved a very favorable subject for the study 

 of the axial row divisions in the ovule. Besides being very small, 

 the ovules are not readily separated from the placental attach- 

 ments, and it is almost necessary to section the entire ovary. 

 Moreover, the developing ovules are bent, and it is difficult properly 

 to orient them so as to have the archesporial axis in a desired plane. 

 Innumerable sections have afforded me only some of the salient 

 stages, sufficient, however, to demonstrate the general method of 

 the reduction divisions. It was very manifest that the reduction 

 divisions did not take place in the embryo-sac, owing to the ab- 

 scnce of the characteristic prophase appearance in its nucleus. 

 Moreover, since all of the gamopetalous dicotyledons yet worked 

 upon have no tapetum and only an axial row of four cells devel- 

 oped from the archesporial cell,* in an}' of these plants where 

 such uniformity seems to exist it seemed of interest to study the 

 divisions in the formation of the axial row. Details of the general 

 macrosporic development have already been given, and here only 

 division phenomena will be briefly discussed. 



The resting nucleus of the Initial cell is at first much like that 

 of the underlying growing cells of the nucellus. The nucleolus is 

 then relatively small and readily loses the gentian stain for the 

 orange. There is a loose reticulum of linin threads, and upon 

 this a considerable number of large granules taking the chromatin 



stain 



As in the nuclei of the pollen mother-cells, synapsis is mani- 

 fest at an early prophase stage. It is marked by the usual con- 

 traction of the linin ribbon, which is always in contact with the 

 nucleolus on one side. The whole mass is usually in the center 

 of the oval nucleus, the nucleolus in this case being in contact 

 with the nuclear membrane, as in Fig. 34. 



The archesporial cell has attained considerable length when the 

 nucleus enters upon the spirem stage. The return from the con- 

 dition of synapsis is especially marked by much better staining in 

 the general ribbon. The ribbon is somewhat thicker than before. 



Straslnirger, Angiospcmien und Gymnospemaen. 



