28 MEYEN ON VEGETABLE IMPREGNATION 
the embryo-sac, which is so exceedingly easy to observe in 
hundreds of other plants, I have never been able to perceive 
in Viscum; probably the membrane of the pollen-tube is here so 
delicate that it is destroyed in preparing the section. The em- 
bryo-sac gradually increases in size from its first appearance to 
the complete development of the embryo, and its impregnation 
manifests itself in the following manner: at first the germ- 
vesicle appears in the micropyle-end of the sac; and nearly 
all round this vesicle is formed an opake and somewhat gra- 
nular mucous substance, which constitutes the commencement 
of the fluid albuminous body. With the appearance of the 
germ-vesicle, however, there occurs likewise a remarkable 
change of the embryo-sac, which divides, by the formation of a 
greater or less number of septa, into many large cells, as may 
be seen in the annexed drawings. The origin of these cross 
septa commences at the upper end of the embryo-sac, where the 
young embryo is situated; and more and more of them are 
gradually formed from above downwards, as shown in the 
figures 6 to 9. About the middle of June the embryo-sac is 
usually divided into eight, nine, or ten large cells, and there- 
upon usually begins the division of these large cells by longitu- 
dinal septa, as represented in fig. 2. Pl. II. at hh, 17, &e. Some- 
times some horizontal septa are likewise formed in an oblique 
direction as at d, fig.8. Pl. I. In some early and strong plants, 
I found as early as the 16th of June, the embryo-sac divided 
by these horizontal septa into from fifteen to sixteen large cells ; 
and these again separated by longitudinal septa into smaller 
cells. In the drawings of the embryo-sacs of the 16th and 19th 
of June, in figs. 8 and 9. Pl. I., there is seen, in almost every 
large cell, a cellular nucleus, and in many cells even several 
such; but in these nothing is more easy to observe than that 
the commencement of the formation of these cellular nuclei is 
subsequent to the formation of the large cells; and, conse- 
quently, that the cells cannot have been formed by this cellular 
nucleus. After the embryo-sac has in this manner become di- 
vided into smaller cells, the formation of the albuminous body 
takes place in them; and this is effected in the manner already 
known, more and more solid substance forming in the limpid 
fluid, which conglomerates into larger or smaller globules, 
around which the cellular membranes harden; and thus a deli- 
cate cellular tissue originates in the interior of those large cells’ 
