100 VEGETABLE ORGANOGRAPHY. 



a multitude of examples of organs which are downy in- 

 their infancy, and which become even smooth in their 

 adult state. 



We cannot deny that hairs are, in several cases, a 

 shelter from external moisture : thus, when we plunge 

 into water the leaves of the Raspberry, for example, we 

 see that the inferior surface, thickly covered with very 

 small hairs, comes out of it without being wetted, 

 because these small hairs retain upon the leaf a stratum 

 of air which protects it from the immediate contact of 

 the water. Most downy surfaces present this pheno- 

 menon in a more or less distinct degree. It is remarkable 

 that most smooth surfaces have some other means of 

 protection against wet — as, for example, being covered 

 with a glaucous powder, or wax, or slimy, oily, or \dscid 

 substances not miscible with water. 



Lastly, there are cases where hairs evidently serve for 

 protection either against insects or wet; thus, for 

 example, the calyx of the Labiatae, which is not closed 

 after flowering, presents in the interior little hairs 

 lying down, or with difficulty visible, during the time of 

 flowering, which are raised up or elongated afterwards 

 in such a manner as to close the orifice of the tube, and 

 defend its aperture either from insects or rain. One 

 would be inclined to believe that the stiff" bristly hairs 

 which are found on several plants, are their defence 

 against insects ; and the analogy of certain hairs with 

 stings tends also to confirm it. 



The hairs of plants, then, are decidedly like those of 

 animals — the protecting organs of the surfaces upon 

 which they are developed. They protect them either 

 against an excess of solar light, the variations of the 

 temperature, wet, or sometimes against insects. I 

 know that in each particular case it is not always 

 easy to assign the function of the hairs ; I believe. 



