130 Taylor — A Morphological and Cytological 



synergidae, the other persisting for a short time (Fig. 40). The 

 "filiform apparatus" was very slightly developed. As the flow- 

 ering of Acer saccharinum upon which the writer had counted 

 for the sequence of stages succeeding the entrance of the sperm 

 nuclei, was followed in 1919 by a severe frost and most of the 

 ovules rendered abnormal or infertile, a detailed discussion of 

 the stages in fertilization will be held for another paper. As 

 soon as the triple fusion is accomplished the endosperm nucleus 

 passes up to the middle of the embryosac (Fig. 40). Division 

 does not ordinarily take place till this position is reached (Fig. 

 42). The fertilized egg is even slower to divide, usually holding 

 back till the eight or even the sixteen nucleate stage of the endo- 

 sperm. The first wall is transverse (Fig. 41), and so is the 

 second, but the third is vertical or oblique in the terminal cell 

 (Fig. 43), and is followed by a similar wall in the middle cell of 

 the original row (Fig. 44). The basal cell seems to divide once 

 more (Figs. 45, 46), and in the later development of the embryo 

 may divide a few times to give the irregular group of cells which 

 form the suspensor of the embryo. The endosperm never be- 

 comes more than a sheath of protoplasm in which the free nuclei 

 divide, at first by mitosis, and later amitotically. They become 

 very numerous, reaching many hundreds. The cavity of the 

 embryosac increases greatly after fertilization, and the nucellus 

 stretches to accommodate it. This condition is especially 

 marked in Acer saccharinum and Acer platanoides. In the 

 latter the contents of the nucellar cells appear disintegrated, 

 and the walls themselves later in part break down, so that by 

 the time the embryo has reached the stage of the Red Maple 

 embryo shown in Fig. 47, the cavity of the embryosac will have 

 increased in volume a hundred times, and be surrounded by 

 only a very few layers of stretched nucellar cells, except just 

 above the micropyle, where the stretching and disintegration 

 does not occur. The embryo occupies only a very small part 

 of the pointed micropylar end of this cavity, and the rapid growth 

 of the sac and disintegration of the nucellus is therefore not due 

 to pressure from the embryo. The outer part of the second 

 integument becomes hardened, protecting the embryo, especially 

 in some of the exotic forms. The rapid growth of the embryo, 

 though delayed, causes the cotyledons in many species to become 

 crumpled in the seed. Evidence of the beginning of this con- 



