1^8 VEGETABLE ORGANOGRAPHY. 



and peduncles, upon the external surface of pericarps, 

 but very rarely on the internal ; the valves, however, 

 of the fruit of Jacksonia afford an example of this. 

 The Hairs of Seeds ought rather to be placed in the class 

 of Scaly Hairs. Some corollas bear lymphatic hairs, and 

 others have corolline ones. 



The general position of Lymphatic Hairs, then, upon 

 parts exposed to the air, proves that the use of these 

 organs is connected with the atmosphere. 



They are in general rare in plants which grow in the 

 shade, or in rich and moist places ; and are completely 

 absent in those which are etiolated, or have been grown 

 in the dark : on the contrary, they are more abundant, 

 generally, in those vv^hich grow in warm and dry places, 

 much exposed to the sun. 



From these facts it has been generally concluded, that 

 the Lymphatic Hairs are evaporating organs; for they are 

 found in small quantity in plants which evaporate little, 

 and in great abundance in those which evaporate much. 

 I confess that I am led to draw a contrary conclusion, 

 and to believe that the hairs are natural obstacles to 

 evaporation, because they defend the parenchymatous 

 parts from the action of the solar light, which is the 

 chief agent of evaporation. We know, therefore, the 

 reason why they are wanting in plants, or parts of plants, 

 which are placed in circumstances little favourable to 

 evaporation ; such as those which are etiolated, and also 

 those that are succulent and aquatic, which have few or 

 no stomata ; or those growing in shady places which im- 

 perfectly receive the action of the sun. On the con- 

 trary, they are very abundant in plants exposed to the 

 full solar action, and which would be dried up by a too 

 powerful evaporation. 



I am confirmed in this opinion by comparing the Hairs 

 with the Stomata; these two organs, although they 



