146 FRANCIS E. LLOYD AND CHARLES S. RIDGWAY 



Tropfen auf der Druse (I. c, 10, 11). This description is accom- 

 panied by a figure (his fig. 5) of the tip of a "nectarial thorn" of 

 Opuntia arborescens, represented as a solid object. Sections of 

 the structures in question are not reproduced. In a discussion 

 of the matter which the senior author had with Professor Ganong, 

 the latter took the position indicated by the above quotation, 

 upon which they fell into amicable disagreement, the senior author 

 maintaining that, in contravention with the many known cases 

 in which the secretion of oils, resins, and the like occurs between 

 the outer cell wall of the epidermis and its cuticle, that of nectar 

 in the Cactaceae is accompanied by a release of the whole epider- 

 mis. In the present paper is offered evidence which shows that 

 each in part was right. 



Echinocactus uncinatus* (figs. 1 to 5). Of the glands which we 

 have examined, that of this species in .particular, on account of 

 its large size, presents great ease of examination. It is dome 

 shaped, supported on a thick pedestal in which the vascular 

 tissues supplying the glandular tissue proper spread out (fig. 1). 

 Surrounding the gland are numerous trichomes which fill the 

 sulcus of the mamilla with a dense felt. Many of them are lignified 

 and it is probable that their numbers increase with the age of the 

 mamilla. The body of the gland is composed of cells, which, at 

 its base, are nearly isodiametric. Above the base they are 

 elongated (fig. 3), and gradually become thicker-walled as the 

 apex is approached. Here they are again isodiametric and have 

 the thickest walls. 



The epidermis as it ascends the base of the gland becomes 

 markedly thicker, this being due to increase in the thickness of 

 the outer wall, and this again especially to the marked increase 

 in the thickness of the cuticle. This thickening, accompanied by 

 cutinization, is extended also into the radial walls (fig. 3) through- 

 out the greater extent of the tissue. Areas occur, usually at the 

 tip of the gland, but elsewhere also, where this thickening of the 

 radial walls does not occur (fig. 4). It is further important to 

 notice that the cutinization may pass entirely down to the inner 



3 No. 10, Cacti of Northern Zacatecas, collected by F. E. Lloyd and deposited 

 in the National Herbarium. 



