354 TRANSACTIONS AND PROCEEDINGS OF [Sess. lvi. 



A. Early Stage. 



In a young ovule (tig. 1) we may readily distinguish a 

 differentiation of cells into a protective layer or dermatogen 

 {derm.), a generative layer or periblem (periU.), and a conduc- 

 tive axis or plerome {pier.). 



The dermatogen does not show anything peculiar except 

 the slightly elongated shape of the cells at the apex. 



The periblem-cells are evidently much elongated radially, 

 abutting with one end on the plerome-axis and with the 

 other end on the dermatogen. The central peribleni-cell 

 (xx) forming the direct elongation of the plerome is the 

 physiological archesporium, i.e., the cell which will perform 

 its physiological function of ultimately giving rise to sporo- 

 cytes. It is surrounded by a number of non-physiological 

 archesporia, which, for reasons we shall understand better 

 afterwards, do not perform their physiological function of 

 developing into sporocytes. 



The terminal plerome-cell shows a number of facets, each 

 of which corresponds to the basal end of a periblem- cell. 



In a slightly more advanced stage (fig. 2) the ovule has 

 commenced to curve downwards and the true archesporium 

 (A.S.), now evidently the largest cell in the ovule, is about 

 three times longer than it is broad; if, however, the carpellary 

 leaf interfere with the downward curvature of the ovule and 

 if it press against the apex of the ovule, the archesporium 

 cannot increase so much in length, but evidently makes up 

 for this defect by attaining a great breadth. In this way 

 we have to account for the difference in the form of arche- 

 sporia (A.S.) seen in figs. 2 and 5, as compared with those 

 shown in figs. 3 and 4. After the archesporium has 

 attained a si/e as in figs. 2, '.), its lateral walls lose their 

 straight outline and l)egin to bulge out (figs. 4 and 5), 

 without producing, however, any visibly injurious effects on 

 the ])criblem-cells surrounding it. The nucleus keeps step 

 with the increase in size of the archesporium (lig. 4), almost 

 touching the hit(3rid r)r periclinal walls, wliile tlie nucleolus 

 remains small. 



JJuring division llic niiclcus gives rise to a large monaster 

 (fig. o), one jjole of which is i)hiced very close to the derma- 

 togen, while the otlier j^oh; is jdaecd at some distance from 



