IN ORCHIDEiE AND ASCLEPIADEiE. 539 



It appeared, however, in Boiiatea, which was also the 

 plant most particularly examined, tliat they tirst become 

 visible soon, but not innnediately, after tlic 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 inmiediate vicinity of 

 the pollen tubes, from which they are with dilficulty dis- 

 tinguishable, 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 thes6 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 })ollen tubes, 

 but by an increase in their number, in a manner which I 

 do not attempt to explain. 



The only other mode in wdiich 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 })ossil)le. 



The obscurity respecting the origin of these nnicous 

 tubes does not, however, extend to their gradual in- 11^2 

 crease and progress, both of which may be absolutely 

 ascertained. 



In Bonatea they are, in the first stage of their pro- 

 duction, confined to the stigma, with the proper tissue of 

 which they are more or less mixed. Soon after they may 

 be found on the anterior protected surface of the style, at 

 first in small numbers ; but gradually increasing, they 

 form a mucous cord of considerable size, in which very few 

 or none of the utriculi of the stigma are observable. This 

 cord, which is originally limited to the style, begins, 

 though sometimes not until several days have elapsed, to 

 appear in the cavity of the ovarium, where it divides and 

 subdivides in the manner I have described in my pa|)er, 



