OP LEAVES. 33 



it generally forms but a part of other and more 

 important deviations. '^ 



Adhesion of leaves by their surfaces. The imion 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 wallflower and in lettuce and cabbage leaves ; 

 other instances have been mentioned in Saxifraga^ 

 Gesnera, ^c} 



In these cases, owing to the non-development of the 

 intemodes, 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 

 Caucalis leptophylla^ the bracts of which were soldered 

 to the outer surface of the flowers. M. Bureau^ men- 



> Wydler, ' Flora,' 1852. p. 737, tab. ix. 



ifl. Ter. Veg.,' p. 254. 



' Bull. Soc. Bot. Fr.,' 1857. p. 451. 



3 



