86 Mr. Hassall on the Stigma in Campanulaceas, ti^c. 



M. Brongniart states, "that the pollen grains undergo no 

 modification either during their appUcation to the hairs or when 

 drawn along vA\h them in their retractile movement, and con- 

 sequently no connexion exists between them and the interior 

 of the style." From this it follows, that fertilization can only 

 take place through the medium of what are considered to be 

 true stigmas, viz. the internal surfaces of the three (occasion- 

 ally four) diverging rays on the top of the style. This state- 

 ment is wholly opposed to tlie result of my investigations. 

 The outer of the mass of pollen grains adherent to the hairs 

 certainly suffer no material change ; but if those in contact 

 with the style be examined, a single pollen tube of consider- 

 able length may be observed to pass from the greater number 

 of the granules, apparently losing itself in the tissue of the 

 style, which I believe it to penetrate through the interspaces 

 between the hairs. I'his view of the matter is further sup- 

 ported by the following corroborative evidence. 1st. The 

 great mass of pollen collected on these hairs, contrasted with 

 the small quantity, or even occasional absence of it, on what is 

 called the true stigmatic surface. 2ndly. The structure of the 

 surface itself — it being covered with papillfe resembling the 

 hairs themselves in all save length. 3rdly. That this surface 

 sometimes does not expand, and when it does, frequently 

 but to a small extent, and this only when the process of fertili- 

 zation is evidently far advanced, and the flower itself some- 

 times even beginning to fade. 



From the obsenation of these facts, I have come to the 

 conclusion, that not only the surface of the true stigma, but 

 more particularly of that portion of the style itself which is 

 covered with hairs, is essentially concerned in the fecundation 

 of Campanulaceag. 



These collecting hairs are by no means peculiar to the Cam- 

 panulae, but exist in the whole of the family Compositae, and 

 in many genera of other orders. I have observed them in Col- 

 lomia grandiflora, Veronica chamcedrys, Hyacinthus orientalis, 

 Ixia maculata, Haivorthia radula, Godetia rubicunda, and 

 Epilobium hirsutum. In the Compositae they are admirably 

 adapted to the office they are destined to perform, viz. that of 

 harrowing up the pollen grains, being all sloped upwards and 

 terminating in a sharp point. These hairs in Haworthia ra- 

 dula cover the true stigmatic surface, are longest near the cir- 

 cumference, and become mere papillae towards the centre of the 

 stigma. In Veronica chamcedrys they also cover the stigmatic 

 surface, but a depression is to be observed in the middle free 



sequence of the loss of their support. — Adolphe Brongniart speaks of this 

 retraction of the hairs as presenting a phienoiuenon unexampled in the 

 vegetable kingdom. 



