Corda on the Impregnation of Plants. 323 
_ her Dotter (vitellum,) (Tab. 44; fig. 35—37, vi.) This vitellum I 
consider to be merely the remains of the pollen-grains which have 
fallen into the micropyle, (the exostome.) 
The kernel-skin is filled with the albumen, in a cavity of which 
we find the embryo with its circularly-disposed cotyledons, (Tab. 
44, fig. 38, 39, 40, 41, co co,) ordinarily nine in number, with their 
summits all turned inwards and thus enclosing the center.of the em- 
bryo, which bears the name of the embryo-bud, (Tab. 44, fig. 41 
and42, Ee Eg.) Icall the undeveloped summit (Eg Eg,) placed 
in the center of the whorl of the cotyledons, the embryo-bud, be- 
cause it corresponds, not only in form and structure, but also in future 
office, with the terminal bud of Coniferous trees. In the one case 
the point of future growth is surrounded and enclosed by the coty- 
ledons ; in the other, leaves disposed in a similar manner enclose the 
so-named and similarly situated bud. 
I endeavored in vain to detect in the soft embryo, the earliest form- 
ed bundle of fibres (which constitutes the skeleton of the plant,) but 
I could only bring to view a delicate homogeneous tissue, (Tab. 44, 
fig. 42, 43,) with a milky homogeneous fluid filled with white globu- 
lar particles. 
The following positions respecting the mode of impregnation in 
Conifere appear to be established by these observations. 
1. The pollen-tube penetrates into the micropyle, (exostome ;) 
and in Pinus the pollen-grains fall directly into it ; — the im- 
pregnation is immediate. 
2. The pollen-tube passes through the exostome into the endos- 
tome, passes through the cavity of sha secundine, and arrives at 
3. The nucule; extends through the endostome into its cavity ; and 
4. By the ejection of the fluid contained in the pollen-grains into 
the bottom of the nucule gives the first keim (germ) to the formation 
of the embryo. 
5. The Sivtahiisn and Sieshipirndnt of the embryo changes the 
contents of the cellular tissue of the nucule, which becomes fluid, 
and appears to furnish material for the growth of the embryo. 
6. The pollen-tubes remain fixed (to the embryo-sac) sometime 
after impregnation and the commencement of the sant 
the embryo in the latter. 
—I am under great obligations to Lt. J. W. Bailey, Prof. of Chem., &e. in the West Point 
+i. Acad, who has kin — undertaken to copy the greater part of the figures; ee of M. 
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