IN ORCHIDEiE AND ASCLEPIADEiE. 539
It appeared, however, in Boiiatea, which was also the plant most particularly examined, that they tirst become visible soon, but not innnediately, 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 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,
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