RTOs Te 
: Fecundation in Orchidee and Asclepiadee. 741 
cessary, and the action of which, from the diminished viscidity 
of the retinaculum, might be injurious. On this subject I will 
also hazard another remark, that the insect forms in Orchideous 
flowers, resemble those of the insects belonging to the native 
country of the plants. 
The next object I had in view was to determine the first ap- 
pearance and progress of the mucous tubes. 
My observations on the origin of these tubes are not alto- 
gether satisfactory. 
It appeared, however, in Bonatea, which was also the plant 
most particularly examined, that they first become visible soon, 
but not immediately, after the production of the pollen tubes 
from the lobules or grains of the mass applied to the stigma; and 
that their earliest appearance is in the tissue of the stigma, in the 
immediate vicinity of the pollen tubes, from which they are with 
difficulty distinguishable, and only by their being less manifestly 
or not at all granular in their surface or contents, and in general 
having those interruptions in their cavity, which I have termed 
coagula, and which I have never yet met with in tubes actually 
adhering to the grain of pollen. . 
But even these characters, in themselves so minute, might be 
supposed to depend on a difference in the state of the contents 
of the pollen tube, after it has quitted the grain producing it. 
It is possible therefore that the mucous cords may be entirely 
derived from the pollen, not however by mere elongation of the 
original pollen tubes, but by an increase in their number, in a 
manner which I do not attempt to explain. 
The only other mode in which these tubes are likely to be 
generated, is by the action of the pollen tubes on the coagulable 
fluid, so copiously produced in the stigma at the only period 
when impregnation is possible. 
The obscurity respecting the origin of these mucous tubes 
does 
