398 BOTANICAL GAZETTE [may 



which would readily differentiate them. Also under orchard con- 

 ditions the glands on the petiole may be active much later in the 

 season. That there is no relation between the glands in the two 

 positions is further shown by the fact that in some species, as in 

 P. americana, glands are typically absent on the serrations but 

 present on the petiole or leaf base. 



Glands which could not readily be classified as belonging to 

 either the leaf serrations or the petiole were not numerous, con- 

 sequently error from this cause has not entered to any appreciable 

 extent into the statistical classification. There was also little 

 difficulty in determining whether glands were borne on the petiole 

 or leaf base, since in most cases there was no leaf tissue between 

 the glands and the base of the blade. When leaf tissue was so 

 present they were classed as being borne on the leaf base. 



The question now arises as to whether the structure of glands 

 on the petiole is similar to that on the leaf base. Gregory (3) 

 showed that glands borne on the petiole and leaf base in the peach 

 were true glands, the upper part being composed of long rec- 

 tangular cells rich in cytoplasm, and with large nuclei, while the 

 central part is made up of parenchyma cells characteristic of 

 glandular tissue, into which extend ramifications of conductive 

 tissue. The structure of the glands in the plum borne on both 

 the petiole and serrations has been examined on leaves just emer- 

 ging from the bud, and on mature leaves with vigorous active 

 glands, and is found to be similar to that reported by Gregory in 

 the peach. 



The similarity in structure between the glands borne on the 

 petiole and on the serrations led Gregory to suggest that the 

 former arose from the latter. Such an origin would imply that both 

 are of the same rank, and that the tissue of the leaf blade is more or 

 less indeterminate with that of the petiole, and would be in accord 

 with the condition of the petiolar glands in some species of willow, 

 notably Salix lucida (fig. 10), in which the glands are minute, 

 numerous, and crowded together at the leaf base, suggesting a 

 proliferation of leaf tissue along the petiole. 



From these considerations it appears that there is justification 

 for regarding the glands of the petiole, and the larger ones borne 



