AXATOxMY OF TI^AXTS. 217 



receptacle, bundles of spiral and sap-vessels proceed into the 

 germen, disperse themselves through it when it is furnish- 

 ed with partitions, and become united in the central column 

 or placenta. From this central column arise, by the mere 

 act of vegetation, those vesicles I have mentioned ; and at a 

 later period, when impregnation takes place, a new activity, 

 awakened by this peculiar stimulus, is called into action. In 

 some instances, the exterior covering of the germen secretes 

 nectar, because at that time there is an evident overflowing 

 of the mild oxydized mucilage into the germen, 



339. 

 The Pistil is commonly a solid column, but sometimes it is 

 observed to have a hollow space throughout its length, al- 

 though this is always shut at the point in which it passes in- 

 to the germen. On the other hand, the communication be- 

 tween the pistillum and the germen is maintained by means 

 of sap and spiral vessels, which pass into the dissepimentum, 

 into the central column or placenta, and constitute the pas- 

 sage to the ovula. We have already endeavoured to shew, 

 that the number of the pistilla corresponds with the loculi 

 of the germen, and that where the pistillum is single, it has 

 in all probability become so from the union of several pis- 

 tilla, (188.) 



340. 



The structure of the Stigma is as wonderful as it Is sim})le. 

 Universally, wherever we have examined it, we have found 

 its surface moist, and studded with very fine warts or hairs, 

 which are always closed as in the roots. Whatever, there- 

 fore, passes into the interior of the stigma, or pistillum, must 

 in this case also make its way through the impervious and 

 shut extremities of these organs. In many plants, particu- 

 larly in the Lobelias, nature has been careful to protect the 

 tender structure of the stigma from external injuries, by a 

 particular contrivance. This is a peculiar veil (Tab. II, 

 Fig. 23.) which covers the stigma, and which, in some gene- 

 ra allied to Lobelia, consists evidentiv of two valves. 



