134 



earliest stages, the embryo sac grows at the expense of the tissue of the 

 nucellus. As it becomes mature it is surrounded by a definite layer of 

 active looking cells, derived from the inner integument, forming a nutri- 

 tive jacket. This stage is characterized by the storage of reserve food 

 to supply the rapid growth which follows fertilization. Starch is de- 

 posited in the placenta and very abundantly in the micropylar region of 

 both integuments. The funiculus contains no starch, since it is the path 

 by which food material enters the ovule and it is important that it should 

 not be blocked by a store of reserve food. 



After fertilization the nutritive jacket becomes even more strongly 

 developed, especially in the chalazal region on the side of the sac nearest 

 the funiculus. The cells of the inner layer have a characteristic appear- 

 ance. They are rounded and turgid, their protoplasm is vacuolated and 

 forms a thick layer lining the inner ends of the cells. They give evi- 

 dence of great activity which would seem to justify the conclusion that 

 they are the cells most concerned at this time in the nutrition of the 

 embryo sac. Later there appears in this region a thick mass of endo- 

 sperm which, acting as an haustorium, rapidly digests and absorbs all 

 tissue with which it comes in contact, and the nutritive jacket is natu- 

 rally the first part destroyed. The location of the starch-bearing and non- 

 starch-bearing areas at this stage seems to justify the following conclu- 

 sions: Food material enters the ovule in solution and is partly stored up 

 and partly passed on to the chalazal region of the embryo sac. Moreover 

 the stored-up food supply is drawn upon by the nutritive jacket in the 

 chalazal region. Starch does not appear in the embryo until just before 

 the cotyledons appear, Avhen a small quantity is found in the base of the 

 embryo and also in the suspensor. In later stages there is a scanty sup- 

 ply of starch in the periblem. 



In the latest stages examined starch was found in varying quantities 

 in all parts of the tissue outside the embryo sac. The ovule, which might 

 now be called the seed, was surrounded by a thick membrane of col- 

 umnar cells extending even across the funiculus. Inside this columnar 

 layer in the region of the funiculus is a flattened, fan-shaped mass of 

 tracheid-like cells of irregular form having reticulate markings on their 

 walls. These absorb food material through the funiculus and pass it on 

 to the surrounding tissues, and especially through a vascular bundle, the 

 raphe, to the chalazal region of the embryo sac. Surrounding the tracheid- 



