148 FRANCIS E. LLOYD AND CHARLES S. RIDGWAY 



ready reaction, with Fehling's reagent, of the solution of a few- 

 droplets taken from the tips of active glands. 



Mamillaria sp. 4 (figs. 9 to 11). This is a species with large 

 mamillae, in which two glands occur in the furrow quite near the 

 rosette of spines. The gland is of peculiar interest in this connec- 

 tion because, when the dissolution of the epidermis begins at the 

 apex of the organ, the first evidence is seen in the separation of 

 the cuticle alone from the cellulose wall (fig. 10). In shape the 

 gland is disc-like, with a slightly concave upper surface, and is 

 raised on a tapering base clothed with long trichomes (fig. 9). 

 Histologically, it is similar to that of the Opuntia described beyond, 

 except that the cuticle is heavier, and that, in harmony with its 

 squat form, the glandular tissue, distinguished by thickened cell 

 walls, is shallow (fig. 9, g), while the underlying, thin-walled non- 

 glandular cells are only slightly elongated. In the epidermis 

 there is neither inner cuticle for any thickening of the radial 

 walls as in Echinocactus, and the cellulose constituent of the outer 

 wall is relatively considerably thicker. 



The first step in the approach of secretive activity is seen in 

 the release of the cuticle covering of some thirty or forty epidermal 

 cells at the extreme apex of the gland. With the material at hand, 

 it is impossible to determine whether there is at this time an accu- 

 mulation of nectar in the hiatus between the cuticle and the 

 corresponding cells beneath. Observation on the fresh material in 

 Mexico led the senior author to the belief that such is not the case, 

 since it was frequently noticed that the tops of young glands showed 

 the presence of air beneath the cuticle. The point is important, 

 but cannot be settled except by more careful examination of the 

 young glands in a fresh condition. 



Very soon after the cuticle begins to be set free, the underlying 

 cells disappear, the cellulose wall being digested (fig. 11), as also 

 the protoplasm. One finds evidence for the digestion of the cell 

 wall in the separation of the cell, not only from the cuticle^but 

 from the middle lamella and from the underlying cells of the gland, 

 and in the thinning and collapse of the cell wall itself. The rate 



4 No. 40, Lloyd. Cacti of Northern Zacatecas. National Herbarium. 



