194 MR. Т. Н. CORRY ON ASCLEPIAS CORNUTI. 
So far, then, there is no direct evidence in favour of self-fertilization under the conditions 
specified. On the contrary, Brown found * that “in the gradual decay of the flower in 
A. phytolaccoides, Pursh., when the parts remained soft, the rupture [of the pollinium] 
and protrusion of tubes took place while the pollen-mass was still in its original position 
immersed in the anther-cell +. The tubes produced in this situation often acquire a great 
length, but coming, immediately on their protrusion from the pollen-mass, in contact with 
the anther-membrane (i. е. the vertical dissepiment), their course is necessarily altered, 
and in their new direction, which is generally upwards, they not unfrequently arrive at 
the top of the anther-cell, or even extend beyond it." I may add that I have repeatedly 
observed exactly the same phenomenon to occur with 4. Cornuti when 041. Inno single 
instance, therefore, even though the pollen-tubes may happen to be produced while the 
pollinium is still ¿n situ, is it possible for them to meet and penetrate the true stigma. On 
the contrary, they are invariably deflected away from it; and a very slight observation of 
the relative position of the parts of the flower as they actually are will convince the 
inquirer that Mr. Pott's idea concerning the adaptation for the purpose of self-fertilization 
of the inner wall of the anther-cell is completely untenable. The part of it which is 
removed on dehiscence never forms a sufficient portion of the whole longitudinal 
length of the wall to permit of any other fate for the pollen-tubes, in case they are 
produced, than that of deflection upwards. These tubes, moreover, arealways produced 
from the inner or more convex of the two edges of the pollinium ; and this edge, when the 
pollinium is % situ, is closely adjacent to the median vertical membranous partition 
separating the two anther-cells, so that the tubes, if produced, would at once encounter 
this, and immediately on their doing so assume an upward direction. Any idea, then, 
that self-fertilization either takes place ог is possible, when the pollinium is still im situ, 
must be erroneous ; for it both has been and can be shown, from the position of the parts 
as well as by direct experimental evidence, that it cannot occur. 
If they are not disturbed, insects often remain for a long period, often for entire hours, 
on the same umbel, and in consequence they search a large number of flowers on the 
same plant before flying to another. This was observed by Delpino to be especially so in 
the case of Scolia hortorum; and I have seen it in the case of the hive-bee. Hence it at 
any rate appears to be possible :— 
(1) That the pollinia extracted from the anthers of a given flower may be inserted into 
the lower portion of other alar chambers of the same flower; and 
(2) That the greater part of the pollinia inserted into the alar chambers of any given 
umbel belong to and were previously extracted from the flowers of that same umbel. 
* Misc. Bot. Works, vol. i. p. 529. 
+ Vide Atlas, plate xxxv. fig. 11, and Linn. Trans. vol. xvi. 
+ Charles Darwin has observed the emission of pollen-tubes from the pollinia while still within the anther and not 
in contact with the stigma in semimonstrous flowers of Malaxis paludosa, Sw., and of Aceras anthropophora, В. Br., 
also in perfect flowers of Neottia Nidus-avis, Rich., three widely distinct Orchid genera, which are, in nature, all 
cross-fertilized, though the last mentioned seems to possess the power of self-fertilizing itself in some degree if insect 
visitors fail it. Vide * Fertilization of Orchids,’ 2nd edit. p. 258. This feature is also general in cleistogamio flowers. 
Vide * Forms of Flowers,’ p. 337. Hofmeister (Neue Beitrüge, ii. pp. 642, 643) has further observed that the pollen- 
grains of Navas very often develop long tubes while lying in the loculi of dehisced anthers. 
