Fecundation in Orchidea and Asclepiadece. 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 1 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 



