CONTRIBUTIONS TO BOTANY. 
147 
there is alwaj's a pervious aperture in the putamen, whether it 
be coraeous, as in Rhus, or thin and fragile, as in Comocladia , — 
whence, from the position of the ovules and the absolute want 
of any placentary communication between the style and the 
ovule, we must infer either that the means of fertilization of the 
latter could only have been conveyed through the spiral vessels 
of the umbilical cord, according to the long-exploded notions of 
Adanson and Turpin, or that it took place by the direct action of 
pollinic boyaux which had found their way to the nucleus through 
the aperture in the apex of the carpel, somewhat in the same 
manner as happens in Gnetacea. As in that paper I have quoted 
the evidence of St. Hilaire regarding the similar mode of impreg- 
nation witnessed by him in Polygonacea, Chenopodiacem, and 
other families, I need do no more than allude to them as additions 
to the mass of evidence here brought together to show that this 
mode of ovular impregnation is more general than is supposed. 
In regard to the remarkable growth of the tubillus in the 
Gnetacea, I am able to cite two analogous instances in families 
of a much higher degree of organization, where the mouth of 
the tegmen is produced into a long tubular expansion, showing 
that such expansion is in no way connected with the develop- 
ment of what have been held to be naked seeds. I have already 
demonstrated its production in the tegmen of the seed of Ha- 
lesia, where the summit of that integument becomes contracted 
into a slender filamentous tube, which appears like a false sus- 
pensor, at the radicular extremity of the seed; here, however, 
the testa closes over it, so that the tubillus, reflected and free, 
lies between the two integuments*. The other instance is still 
more striking, and exists in Tropaolum, in which genus the pro- 
duction of its tubillus remains to this day an enigma among 
botanists. The fact of its occurrence was, I believe, first noticed 
by Gaertnerf, and afterwards by St. Hilaire J, who considered it 
to be a suspensor analogous to that of Cycas, and the channel 
through which the aura seminalis was conveyed from the funicle 
for the fecundation of the ovule. Dr. Giraud, in tracing the 
development of the ovule of Tropaolum majus, and the mode of 
its fertilization by the impact of the pollen-tube upon the apex 
of the nucleus, confirmed the observations of St. Hilaire in re- 
gard to the production of the tubillus at the micropyle of the 
inner integument § ; he also considered this process to be a sus- 
pensor like that of Cycas, which he regarded as an expansion of 
the embryo-sac. Schleiden also demonstrates the same fact ||, 
* Contributions to Botany, i. 169, pi. 31. fig. 23. 
t De Fruct. i. 380, tab. 79. fig. 1. + Ann. Mus. xviii. 469. 
§ Linn. Trans, xix. 164, tab. 16. figs. 5, 6, 7, 8. 
II Nov. Act. Acad. Leop. .xix. 54, tab. 8. figs. 120-125, p. 56, fig. 126. 
