Corda on the Impregnation of Plants. 321 



We left the pollen-tubes when they had reached the endostome 

 of the secundine. In order to ascertain how far the pollen-tubes 

 penetrate, I made a longitudinal section of an ovule, while yet en- 

 closed in the scale, in such a manner (Tab. 43, fig. 14,) that a great 

 part of the secundine was removed, while the nucule (/) and the 

 embryostome (/') were left entire ; by this means the course of each 

 pollen-tube {a') was manifest from the endostome (e^) to the very 

 bottom of the nucule (a^.) 



I saw the pollen-tubes pass through the orifice of the secundine 

 to the mouth (the embryostome) of the nucule (/'') ; pass through 

 the latter into the cavity of the nucule, where they become some- 

 what attenuated, or suddenly enlarge, (Tab. 43, fig. 14, a',) and 

 empty their contents as a turbid, originally amorphous, fluid mass. 



After this deposition, the pollen-tube still remains in the endos- 

 tome, the embryostome, and the cavity of the nucule, appearing as 

 a slender, empty, and transparent bag. The deposited matter is 

 soon perceived to become organized, and the sac of the embryo 

 (Tab. 43, fig. 15, E) is formed, which increasing rapidly in size, 

 often appears flaccid, or thrown into folds on one side or the other ; 

 and its contents are still turbid. It is still fixed to the pollen-tube, as 

 we have represented in Tab. 43, fig. 15 — 18, E a'. 



During the growth of the sac of the embryo a peculiar change 

 takes place in the minute polyhedral bodies which occupy the cells 

 of the tissue of the nucule ; these particles become fluid or disap- 

 pear as it were by absorption, until the cells again appear perfectly 

 clear and pellucid, (Tab. 43, fig. 18.) 



At this period there may be found, especially in Finns Abies, 

 more than one embryo-sac in each ovule ; there are ordinarily two 

 or three placed side by side,* (Tab. 42, fig. 7, 10, 11.) These 

 embryo-sacs are found, on examination, to consist of an integument 

 (Tab. 42, fig. II, p) loosely enclosing a kernel (q.) The kernel 

 has a gelatinous consistence, and is composed of large, oblong cells 

 (Tab. 42, fig. 12,) mixed with fine knotty threads, to which minute 

 drops of a fluid adhere, (Tab. 42, fig. 13, m n.) The connexion of 

 the pollen-tubes with the embryo-sac continues for some time after 



* The fact of the general existence of a plurality of embryos in the impregna- 

 ted ovule of Coniferse and Cycadeae was announced by Dr. Brown to the British 

 Association at their meeting in Edinburgh in 1834, a few months previous to the 

 date of this paper, which was read Sept. 1834. This announcement was, of course, 

 unknown to M. Corda at that time. — Trans. 



Vol. XXXL— No. 2. 41 



