NUCLEUS OR KERNEL. 
340 ALBUMEN. 
any change is apparent in the oosphere, a number of cells are 
produced by free cell-formation (see Cell-development) in the 
protoplasm of the embryo-sac around the embryo. These cells, 
which contain nutritive matters of various kinds, especially 
designed for the nourishment of the embryo developed in the 
sac, form what is usually termed endosperm. In the Gymno- 
spermia the endosperm is formed before fertilisation. The cells 
existing outside the embryo-sac, or those of the nucellus gene- 
rally, also become filled with starch and other nutritive material 
in rudimentary seeds, and form what has been called the peri- 
sperm. 
; The embryo, by absorbing the nourishment by which it is 
surrounded, begins to enlarge, and in so doing presses upon the 
parenchymatous cells by which it is enclosed, 
and thus causes their absorption to a greater 
or less extent, according to the size to which 
it ultimately attains. In some cases, the 
embryo continues to develop until it pro- 
duces the destruction, not only of the paren- 
chymatous tissue within the embryo-sac, as 
well as the sac itself, but also of that of the 
nucleus, and it then fills the whole interior of 
the seed, and is coated directly by the integu- 
ments. But at other times the embryo does 
Fic. 762. 
Fig. 762. Vertical 
section of the seed 
of the White Wa- 
ter-lily, showing 
the embryo en- 
closed in the re- 
mains of the em- 
bryo-sac or vitel- 
lus, and on the 
outside of this 
the albumen sur- 
rounded by the 
not develop to any such degree ; in which case 
it is separated from the integuments by a mass 
of parenchymatous tissue of varying thickness 
which may be derived from that of the nucleus 
itself, or from both that of the nucleus and 
embryo-sac according to the extent to which 
the embryo has developed. To the tissue which 
thus remains and forms a solid mass round the 
integuments, 
< embryo, the name of albumen has been com- 
monly applied ; but as the nature of this substance is different 
from that called by chemists vegetable albumen, it is now often 
designated as the perisperm or endosperm according to its origin 
as described above. Both endosperm and perisperm may be seen 
in the Nymphea (figs. 757 and 762). The general name of albu- 
men will be alone generally employed in future in this volume, 
as it is the one best understood, and so long as we recollect its 
origin and nature, the adoption of such a name can lead to no 
confusion. 
From the above considerations it will be evident that the 
nucleus of the seed may either consist of the embryo alone, as 
in the Bean and Pea (fig. 748); or of the embryo enclosed in 
albumen, as in the Poppy (jig. 775), Pansy (fig. 774, al), Oat 
(fig. 705, a), and Nymphexa (fig. 762). We have two parts, 
therefore, to describe as constituents of the nucleus, namely, 
the albumen and the embryo. 
