198 MR. T. H. CORRY ON ASCLEPIAS CORNUTI. 
observations have been made in America upon the fertility of any Asclepias living under 
its natural conditions, and I cannot, in consequence, speak definitely upon this point, 
although, judging from Delpino’s experiments in Italy and my own in this country, I 
believe that it is not so. I have fertilized flowers of 4. Cornuti with pollinia taken from 
other flowers of the same individual plant, from flowers of plants also which had been | 
propagated by buds from the same stock though growing on separate roots, and finally 
from flowers of а distinct individual raised from seed; in the last case alone was the 
result successful, while in the two former, though the pollen-tubes were produced and 
penetrated as far as the ovary, no seeds resulted. Delpino’s results are in complete 
accordance with my own; he fertilized some flowers with their own pollinia, others with 
pollinia extracted from the same umbel, others with pollinia taken from a different 
umbel on the same plant, and last of all, some with pollinia taken from a different indi- 
vidual which he believed to have been propagated by budding from the same individual. 
In every case the plant was equally sterile, and no seeds resulted, although in all the 
skein of pollen-tubes was produced, and he regards the infertility as due to the want of 
thorough cross fertilization, i.e., by the pollinia of a perfectly distinct individual. That 
the self-sterility depends solely on the diminished degree of efficiency of the pollen in 
` self-fertilization of any kind in this species is, I think, clear, since it cannot and does 
not depend on either the pollen or the ovules being in an unfit state for fertilization ; for 
both have been found effective in union with other distinct individual plants of the same 
species. The penetration of the stigma and style by pollen-tubes in the cases of sterility 
is, moreover, not a unique phenomenon only to be met with in Asclepias *. Hildebrand 
has observed in Corydalis cava that the plant was absolutely sterile to its own pollen, 
though the pollen-tubes penetrated into the tissue of the stigma; and Mr. John 
Scott + found the same to be true of two species of Orchids, Oncidium sphacelatum 
and O. microchilum, though in all three cases it produced good seed when fertilized 
by pollen brought from a distinct individual, while its own pollen was in every way 
normal. 
By raising plants of 4. Cornuti from seed, and exposing them near together in open 
situations, we get fruit produced and seed set ; for this is the natural process. It is worthy 
of note that those flowers which are not pollinated, long remain fresh, while those which 
have been pollinated, but in an ineffectual manner, become disarticulated and fall off a 
few days after it has taken place. 
2. FECUNDATION. 
When the pollinium has been placed in the stigmatic portion of the alar chamber, the 
following changes take place :—The pollinium is torn or foreed open from within, first 
at the most prominent point of the edge, which is next the stigma, the rupture gradually 
extending for about a third of the entire length of the pollinium. The portion through 
which this rupture extends is usually the middle third, both the inferior and superior 
extremities of the edge remaining entire. Sometimes, however, the rupture may be seen 
* International Horticultural Congress, London, 1866, T Proc. Bot. Soc. of Edinburgh, May 1863. 
