150 On the Reproductive Functional [No. 3, 



into the apparent cause, as in certain cases we find it arising from the 

 non-emission or non-penetration of the pollen tubes ; the pollen through 

 some mysterious cause being thus utterly impotent on its own stigma. 

 The results of my present examination will, I trust, be found of sufficient 

 interest to permit of my stating them here. They are as follows : first, I 

 applied the pollen of each of the three varieties, reciprocally, to their 

 stigmas ; on dissecting these, I found them abundantly permeated 

 by pollen tubes, many of which I distinctly traced into the ovary. 

 Secondly, I fertilised several flowers in each variety, with its own 

 pollen ; on examining the stigmas of a few of these flowers, I found 

 that many of the pollen grains had emitted tubes, but comparatively 

 few had penetrated the stigmatic tissue, and of these still fewer 

 permeated the conducting tissues of the styles. Several of the latter, 

 however, I traced into the vascular bundles of the placenta, the 

 pistillary cords, and in one or two instances, I believe that I detected 

 them in the nucleus of the ovule. Nevertheless we have seen that, 

 though these pollen tubes are developed, they most ineffectively 

 perform their deputed function, inasmuch as not one of these matured 

 even a single ovary ! I have here to observe, however, that these 

 pollen tubes do not seem utterly void of the fecundative influence, as 

 many of the ovaries did undergo a certain degree of development ; and 

 on examination of these, as they dropped off, I found that the ovules 

 also had undergone a partial and variable degree of development. In 

 general, the fleshy albuminous envelope of the embryo was largely 

 developed, whereas the embryo had undergone a very slight develop- 

 ment, judging from a comparison of other good seeds of a similar stage, 

 not at all proportionate to the size attained by the albuminous parts. In 

 nearly all the embryos which came under my observation, the develop- 

 ment had ceased ere they exhibited any distinct separation of parts ; a 

 few only had reached that stage in which the axial and lateral 

 projections were visible. 



We thus see, that whatever be the real cause of the inveterate self- 

 sterility of the three varieties of the V. phoeniceum, it does not arise, 

 as has been shown in other cases, from the non-emission of the pollen 

 tubes. In these, as I have elsewhere noticed it, in certain individual 

 plants of different species of Oncidia, Maxillaria, and Passifloras, 

 sterility apparently results from some slight differentiation of the male 



