OF LEAVES. oo 
it generally forms but a part of other and more 
important deviations. 
Adhesion of leaves by their surfaces——'The union of leaves 
by their surfaces is not of very frequent occurrence, 
many of the instances cited being truly referable to 
other conditions. Bonnet describes the union of two 
lettuce leaves, and Turpin that of two leaves of Agave 
americana, in which latter the upper surface of one 
leaf was adherent to the lower surface of the leaf next 
above it, and I have myself met with similar instances 
in the Saliflawet and in lettuce and cabbage leaves; 
other instances have been mentioned in ‘Sazifraga, 
Gesnera, Sc. 
In these cases, owing to the non-development of the 
internodes, the nascent leaves are closely packed, and 
the conditions for adhesion are favorable, but in most 
of the so-called cases of adhesion of leaf to leaf by the 
surface, a preferable explanation is afforded either by 
an exuberant development (hypertrophy) or by chorisis 
(see sections on those subjects). Thus, when a leaf of 
this kind is apparently so united, that the lower surface 
of one is adherent to the corresponding surface of 
another, the phenomenon is probably due rather to extra 
development or to fission. There is an exception to 
this, however, in the case of two _ vertically-erect 
leaves on opposite sides of the stem; here the two 
upper or inner surfaces may become adherent, as In an 
orange, where two leaves were thus united, the ter- 
minal bud between them being suppressed or abortive. 
Adhesion between the membranous bract of Narcissus 
poeticus and the upper surface of the leaf is described 
by Moquin.*” The same author mentions having seen a 
remarkable example of adhesion in the involucels of 
Cauealis leptophylla, the bracts of which were soldered 
to the outer surface of the flowers. M. Bureau* men- 
* Wydler, ‘ Flora,’ 1852, p- (ad, tab. 1x. 
; ‘EL. Ter. Veg.,’ p. 254. 
* Bull. Soe, Bot. Fr.,’ 1857, p. 451. 
