154 FRANCIS E. LLOYD AND CHARLES S. RIDGWAY 



the cell wall, it may be more particularly the primary wall. Re- 

 search in this direction would not be amiss. 



SUMMARY 



The nectar glands of the Cactaceae, so far as they may be repre- 

 sented by Echinocactus, Opuntia and Mamillaria, are of a type 

 in which secretion of nectar is preceded by digestion of the epider- 

 mal cells, and consequent disorganization of their walls and con- 

 tents. This sets free the whole outer wall of the epidermis, from 

 which, however, the cellulose element may disappear. There is 

 thus formed a chamber for the reception of nectar at the top of 

 the gland. The rupture of the membrane sets the nectar free. 

 In Mamillaria and perhaps Opuntia at first only the cuticle is 

 thrown off, but this is only an early expression of the disorganiza- 

 tion of the whole epidermal tissue capping the gland. 



EXPLANATION OF FIGURES 



1 A mature nectar gland of Echinocactus sp., in median longitudinal section. 



2 A portion of the apex of the same gland, showing the somewhat extensive 

 intercellular spaces, and the breaking away of the radial walls. 



3 A portion of the same, with the details of secondary walls and contents 

 of the cells presented in greater detail. The figure is taken from the edge of the 

 area of dissolution of the cells. Droplets of oil are shown in the middle epidermal 

 cell. 



4 Epidermal cells in tangential view, to show the irregularity of cutinization. 



5 The cutinized strands of the inner walls of the epidermis. 



6 Mamillaria sp. (Lloyd, No. 31). The development of the trichomes. 



7 The formation of cork of epidermal origin beneath the trichome pad. 



8 Early cork divisions in the epidermal and sub-epidermal cells, e, Epidermis. 



9 Longitudinal section of the gland of Mamillaria (Lloyd, No. 40). g, Glandu- 

 lar tissue proper; p, Thin-walled prosenchymatic tissue; c, Cork tissue forming 

 the floor of the areolar pad. 



10 Apex of the same gland showing the separation of the cuticle from the apical 

 epidermal cells. 



11 Edge of the area of dissolution in the same, at a later stage. 



12 Gland of Opuntia (Lloyd, No. 46). Letters as above. 



13 The disintegration of the epidermis in the same. 



14 and 15 Edges of areas of dissolution at a later stage. 



