cook: leaves of amygdalaceae 219 



the stipules are distinct from the petiole, and the botanical signifi- 

 cance of this fact is not pointed out. The reader is left to infer 

 that the stipules are attached directly to the branch, for nothing 

 is said of another foliar element below the base of the petiole. 



Without attempting to determine whether this joint in the 

 leaves of the Amygdalaceae is truly homologous with the leaf- 

 articulations of leguminoseae, it is at least to be considered as 

 a vegetative character that sets the Amygdalaceae one stage 

 farther away from the Malaceae and true Rosaceae. Botanists 

 have long recognized a very close approximation between the 

 rosaceous and leguminous series. Such types as Chrysobalanus 

 have often been passed back and forth between the two series 

 by different authorities on classification. Some botanists may 

 not consider tha attachment of the stipules as a sufficient indication 

 that the persistent base is really a part of the leaf instead of an 

 outgrowth from the internode. But it is believed that a com- 

 parison of the stone fruits with other rosaceous types will convince 

 most observers on this point. 



Reduced to the simplest terms of morphology, the leaves of 

 the higher plants, including the monocotyledons, consist of two 

 structural elements, a more or less sheathing base and a more 

 or less expanded blade. The petiole is a secondary specialization, 

 in some cases representing an elongation of the upper part of the 

 basal sheath, in others a narrowing of the lower part of the blade. 

 In the fan-palms the petiole is a part of the leaf sheath, with the 

 ligule at the end, while in Desmoncus and other related genera of 

 Cocaceae, the ligule is below the petiole which evidently repre- 

 sents only the naked base of the rachis. 



In most of the dicotyledonous families the sheathing character 

 of the basal element has been lost, but in this respect the Rosa- 

 ceae, Ranunculaceae and related families are less specialized, so 

 that there can be little question of the homology of the stipular 

 portions of the leaves with the bud-scales and sheaths of Arto- 

 carpaceae, Piperaceae, aroids and palms. 



The leaf-bases of the Amygdalaceae are able to persist because 

 of the joint that allows the petiole to separate and fall off with the 

 blade at the end of the season. At San Antonio, Texas, where 



