202 Ferguson. — Development of the Pollen-tube and the 
of the same ovule would have shown pollen-tubes which had 
pierced to a greater depth into the nucellus. The conditions 
of development as figured for January coincide perfectly with 
those which exist during the latter part of October. 
Growth is very slow during the first period of develop- 
ment, but with the renewed activities of spring the ovule 
increases rapidly in size ; the central cavity of the nucellus 
becomes greatly enlarged and is lined with the growing endo- 
sperm. The prothallium now consists of a uniform layer of 
protoplasm in which numerous free nuclei are embedded, no 
cell- walls as yet having been laid down. Immediately sur- 
rounding the endosperm, there is a definite band or hollow 
sphere of cells which is limited on its outer surface by a thin 
stratum of the disintegrating nucellus. These two layers 
constitute the so-called spongy tissue. The inner portion 
of this tissue, i. e. the prominent band in immediate contact 
with the prothallium, must be intimately connected with the 
nutrition of the young endosperm. The true structure and 
function of this layer seem to have escaped the notice of 
previous writers. Its cells contain large nuclei, and are 
abundantly supplied with protoplasm. The karyokinetic 
figures so frequently observed in these cells show that this 
tissue increases in size by the growth and division of its 
cells, as do the other portions of the ovule. As it enlarges, 
the cells of the nucellus in contact with its outer surface 
become disorganized and are absorbed (Fig. 3). 
The cells of the nucellar cap which were penetrated by 
the pollen-tubes during the previous season do not again 
become active, but remain as deeply staining, thick- walled, 
dead cells. The cells just beneath them, however, multiply 
rapidly, and become literally packed with starch. A few of 
the cells from this region in Fig. 5 are shown more highly 
magnified in Fig. 18. By the growth and increase of these 
cells, the dead top of the nucellus with its pollen-tubes is 
lifted far above the developing endosperm, so that the pollen- 
tubes, once so near their goal, are now removed from it by 
a considerable distance (Figs. 2-4). Meanwhile the pollen- 
