276 On the Morphology of the Organs called Lenticels. 



]\Iohl, that the adventitious roots are only accidentally produced 

 on points occupied by lenticels, and that these roots commence 

 their appearance externally by an elevation of the epidermis, 

 which presents the appearance of a young lenticel and is con- 

 verted into a coleorhiza by the passage of the root, but that this 

 elevation, which never becomes a suberose lenticel, is without any 

 analogy with the lenticular elevation. 



True lenticels had only been noticed on woody stems, but 

 I have ascertained their existence not only upon some herba- 

 ceous stems, and on rhizomes or underground stems, but even 

 on the surface of roots, both of trees and herbaceous plants 

 {Betula alba, Dahlia variabilis, Mirabilis Jalapa, &c.), and fre- 

 quently on the petioles of leaves (as in the Elder). Finally, 1 

 have ascertained that the rugosities which are commonly seen 

 on the surface of the epidermis of some fruits, on the bark of 

 Melons for example, are merely lenticels more or less deformed, 

 and that most of the punctures which exist on the surface of 

 Apples and Pears are lenticels incompletely formed, by the de- 

 struction of an epidermic elevation and the desiccation of the 

 subjacent cellular tissue. 



The lenticel therefore is not an organ without analogy with 

 other known organs j in its first state it passes by insensible 

 gradations to the epidermic productions known under the names 

 of hairs, thorns, and glands. During the following period, after 

 the destruction of the epidermic elevation, it is formed by the 

 hypertrophy of the superficial cortical cellular tissue, a hyper- 

 trophy which appears to be determined by the contact of the 

 subepidermic cellular tissue with the external air. This hyper- 

 trophy differs neither organically nor physiologically from the 

 suberose production of the Cork Oak. The form of the hernia 

 or lenticellar cushion is determined by the epidermic fissure 

 which serves it as a mould ; its form is usually that of a button- 

 hole with thick edges which throw shreds of epidermis out- 

 wai-ds : this form resembles that of the stomata, but it appears 

 to me that the analogy between the stomata and the lenticels is 

 confined to this resemblance. 



The physiological function of the lenticels appears to me to 

 consist simply in causing the commencement of fissures in the 

 epidermis. In consequence of the growth of the tree in height 

 and diameter these fissures become long clefts, ext(!nding either 

 in a vertical or horizontal direction, and facilitate, by loosening 

 the bark, the increase of the diameter of the tree. 



