Morphologie, Befruchtung, Teratologie, Cytologie. 517 



The papillate apical cells of the nucellus project into the micropyle 

 and are later absorbed by the pollen tube. In most of the Alsinoi- 

 deae the pollen tube is thick and persistent becoming twisted on 

 itself before penetrating the synergidae but in Stellaria media it is 

 thin and untwisted. After fertilisation the definitive nucleus divides 

 and gives rise to endosperm nuclei; these divide rapidly at the mi- 

 cropylar and antipodal ends of the sac leading to aggregations of 

 nuclei and dense cytoplasm at these points. The aggregation at the 

 antipodal end gives a distinct impetus to digestion, the embryosac 

 elongating rapidly at the expense of the axile rows of nucellar tis- 

 sue. The micropylar aggregation forms an endosperm cap in the 

 vicinity of the basal suspensor cell. Free cell formation takes place 

 at the first differentiation of the cotyledons and the endosperm con- 

 sists of a Single peripheral layer of cells except at the ends of the 

 sac. The cells of the endosperm cap possess dense homogenous 

 Contents and suggest ferment cells. The author concludes that the 

 endosperm is the medium through which the starch stored in the 

 perisperm is made available for the embryo. 



After fertilisation two or three of the basal rows of the axile 

 cells of the nucellus become cuticularised and form a band across 

 the chalaza. These cells show pores which probably allow free pas- 

 sage of water for the vascular tissue of the funicle does not pene- 

 trate beyond the integuments and there is no vascular tissue in the 

 chalaza. The perisperm after fertilisation forms a tongue of cells 

 with the convex surface pressed against the embryosac; at maturity 

 all the cells contain starch. 



The perisperm exercises a mechanical influence on the shape 

 of the embryosac. Its presence increases the curvature of the em- 

 bryosac and embryo. The peripheral layers of the nucellus keep 

 pace with the growth of the ovule remaining about 4 — 5 layers 

 thick. All are absorbed before maturity, the external layer alone 

 persisting. 



The oospore elongates and forms a haustorium at the micropylar 

 end which projects into the nucellar tissue. The suspensor consists 

 of one large basal cell succeeded by 4 — 6 others. As the embryo 

 grows the basal cell elongates and acts as an absorbent organ. It is 

 finally absorbed by the endosperm cap. The basal suspensor cell 

 reaches it greatest development in the Alsineae\ in the Sperguleae 

 it is little differentiated. The inner integument consists of two cell 

 layers; at first the cells of the apex are large and project beyond 

 the outer integument but they shrivel after the passage of the 

 pollen tube. In the mature seed the two layers fuse into one. The 

 outer integuments consist of two-laj^ers and in the mature seed 

 the cells of the outer layer form projecting papillae. It remains 

 distinct tili the embryo is well advanced then the cell contents des- 

 integrate and the cells become crushed. In Spergula arvensis the 

 wing which surrounds the ovule is formed by the proliferation of 

 the inner layer. Possibly this layer forms a water jacket for the 

 ovule and this may also be its function in Stellaria media. 



Germination in Cerastiiim perfoliation begins by elongation of 

 the cotyledons into the central mass of perisperm. The nucellar 

 cells show a decrease in starch in the proximity of the endosperm 

 cap: the cells of the latter present an actively secretory appearance 

 and are closely connected to the embryo on the one side and the 

 nucellus on the other. The cap becomes pushed slightly outside the 

 micropyle and finally rnptures and persists as a collar. Roothairs 



