EEE EEE GNOME, TES pe. SNE 
306 MR. W. GRIFFITH ON THE GENUS GNETUM. 
becoming necessarily much enlarged, and adhering firmly to the walls of the cavity it 
lines. 
* Although I have repeatedly examined the ovula of Gnetum with a view to the nature 
of their impregnation*, I am not in possession of a single fact relative to its performanee. 
I must, however, mention, that the ovula of Gnetum scandens and lepidotum do not 
appear to be ever submitted to the action of the pollen derived from their proper male 
flowers. In G. Brunonianum this is obviated by the extreme smallness of the annulate 
involucrum. My residence at the Botanical Garden of Calcutta, and the great and un- 
varying kindness of Dr. Wallich, have put me in possession of some, I think, interesting 
facts relative to the impregnation of Cycas, which it may not be amiss to state. I may 
here observe, that the consideration of the mode of application of the pollen-tubes to the 
apex of the nucleus in some plants possessing the ordinary structure of ovarium, had led 
me to suppose that these productions are merely organs of communication, developed on 
account of the distance that necessarily exists in these plants between the stigmatic 
surface and ovulum, and that hence, in Cycas and plants of a similar simple structure, 
in which actual application of the pollen itself to the apex of the nucleus can obviously 
take place, no pollen-tubes would be produced. 
In forming this view, I had not lost sight of the apparent penetration of the pollen- 
tubes into the ovula of Asclepiadeæ, first observed by Dr. Brown; but I supposed that it 
might be the result of the anomalous formation of the nucleus in these cases. Repeated 
observation has since, however, taught me, that not only does application of the pollen- 
granules to the apex of the nucleus of Cycas take place, but that pollen-tubes are like- 
wise generated, although, as might be expected, much shorter than usual. Indeed, the 
tubular membranous portion of the apex of the nucleus becomes actually crammed with 
pollen-granules, from the lower and outer of which pollen-tubes are pretty generally 
produced. | 
The orifice of the envelope of Cycas has a callous and shining appearance; and — 
although I have often examined pollen-grains which had been in apposition with it for — 
some time, I have never seen any production of boyaux, except in the cavity of the apex 
of the nucleus. E 
Although I have by no means proved the necessity of the production of the pollen- — 
tubes in Cycas to ensure fecundation, I consider the fact of their production a strong — 
argument in favour of the idea that actual penetration does occur in every case in which E 
the application of the tubes to the apex of the nucleus can be conceived. The fact of the. ; 
production of the tubes likewise seems to me to put the nature of the bodies from which > 
they originate out of all doubt, and to prove the truth of Dr. Brown's remark (Memo — 
cited, p. 30), that it would be quite gratuitous, on the grounds stated, to consider the par — 
ticles contained in the thecæ to be analogous to the fovilla. E. 
Dr. Brown, in his account of microscopical observations on the particles contained in i : 
the pollen of plants, published in the * Edinburgh Journal of Science,’ vol. ix. p. - 2 
* The opening of the outer coat never presents a shining appearance. 
