Corda on the Impregnation of Plants. 323 



ner 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 raicropyle, (the exostorae.) 



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 

 and 42, E^ Eo-.) I call the undeveloped summit (E^ E^,) 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 

 Coniferae 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 ; whence the im- 

 pregnation is immediate. 



2. The pollen-tube passes through the exostome into the endos- 

 tome, passes through the cavity of the 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 formation and development 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 development of 

 the embryo in the latter. 



Note. — I am under great obligations to Lt. J, W. Bailey, Prof, of Chem., &c. in the West Point 

 Mil. Acad., who has kindly undertaken to copy the greater part of the figures, illustrative of M. 

 Corda's memoir. Tlie figures occupy three plates in the original ; hut by omitting those of minor 

 importance, we are enabled to present in two plates all which are essential to the elucidation of 

 the memoir. The original numbering and lettering of the figures is of course retained.— A. G. 



