I4I8 



A TEXTBOOK OF THEORETICAL BOTANY 



very scarce, though one or two positive demonstrations have been claimed. 

 Indirectly, the presence of starch grains both in the oosphere and in the cells 

 of the young embryo may be accepted as evidence of the presence of starch- 

 forming plastids, while in Podophyllum such plastids have been seen. Chon- 

 driosomes and chondriosome-like bodies have also been seen, but the usual 

 cytological techniques applied to embryo sac study are not adapted to show 

 cytoplasmic inclusions satisfactorily and further observations are required. 



The oosphere nucleus at first is not markedly different from the synergid 

 nuclei, or at most it may be distinguished in being somewhat larger. It has 

 a larger nucleolus which it retains, and as the time of fertilization approaches, 

 it begins to increase in volume. Nevertheless there is apparently always some 

 differentiation of the oosphere nucleus from its neighbours. In the species 

 of Tulipa investigated by Guignard there is no cell formation in the embryo 

 sac but only eight free nuclei, of which two are smaller, placed at the micro- 

 pylar end, and are apparently synergidae. Among the five remaining nuclei, 

 however, the oosphere nucleus is always distinguishable from the others. 

 No case of complete nuclear indifference is known. 



The maturation of the oosphere nucleus is accompanied by a marked 

 reduction in its stainability (Fig. 13 10). This is most observable if the 



Fig. 1210.— Inipatiens iilandiilii^era (I.roylei). Maturation of the oosphere. Feulgen stain. 

 Reduction of the chromatin threads to chromomeres and finally to two chromomeres at 

 maturity (G). H, Mature nucleus unusually swollen. (After Steffen.) 



Feulgen stain for desoxyribose-nucleic acid is used. The chromatin first 

 assumes a prophase-like appearance, then there is a progressive discharge 

 of nucleic acid from the chromosomes, which take on a chromomeric 

 structure. The chromomeres eventually all disappear except for particles 

 which apparently correspond to chromocentres, although they are much 

 smaller than usual. Finally these also may disappear with the exception of 



