unimpregnated Ovulum in Phenogamous Plants. 413 
perforated, is generally acute and more deeply coloured, or 
even sphacelated. | 
The membrane of the nucleus usually constitutes the inner- 
most coat of the seed. But in a few plants an additional coat, 
apparently originating in the inner membrane of Grew, the 
vesicula colliquamenti or amnios of Malpighi also exists. 
In general the amnios, after fecundation, gradually en- 
larges, till at length it displaces or absorbs the whole substance 
of the nucleus, containing in the ripe seed both the embryo 
and albumen, where the latter continues to exist. In such 
cases, however, its proper membrane is commonly obliterated, 
and its place supplied either by that of the nucleus, by the 
inner membrane of the ovulum, or, where both these are eva- 
nescent, by the testa itself. 
In other cases the albumen is formed by a deposition of 
granular matter in the cells of the nucleus. In some of these 
cases the membrane of the amnios seems to be persistent, 
forming even in the ripe seed a proper coat for the embryo, 
the original attachment of whose radicle to the apex of this 
coat may also continue. This, at least, seems to me the most 
probable explanation of the structure of true Nympheacez, 
namely, Nuphar, Nymphza, Euryale, Hydropeltis, and Ca- 
bomba, notwithstanding their very remarkable germination, as 
observed and figured in Nymphza and Nuphar, by Tittmann*. 
In support of this explanation, which differs from all those 
yet given, I may here advert to an observation published many 
years ago, though it seems to have escaped every author who 
has since written on the subject, namely, that before the ma- 
turity of the seed in Nympheacez, the sacculus contains along 
with the embryo a (pulpy or semi-fluid) substance, which I 
then called Vitellus, applying at that time this name to every 
body interposed between the albumen and embryo}. The 
opinion receives some confirmation also from the existence of 
an extremely fine filament, hitherto overlooked, which, ori- 
ginating from the centre of the lower surface of the sacculus, 
and passing through the hollow axis of the albumen, probably 
connects this coat of the embryo in an early stage with the 
base of the nucleus. ; 
The same explanation of structure applies to the seeds of 
Piperaceze and Saururus; and other instances occur of the 
persistence either of the membrane or of the substance of the 
ammnios in the ripe seed. 
It may be concluded from the whole account which I have 
given of the structure of the ovulum, that the more important 
* Keimung der Pflanzen, p. 19. & 27. tab. 3, & 4. 
+ Prodr. Flor. Nov, Holl, i. p, 306. 
changes 
