Subcortical Formation and Abnormal Development of Stomata in Etiolated Shoots of Opuntia Blakeana

Abstract

1. This paper deals with a comparison of the appearance, form, and structure of normal, etiolated, and etiolated-greened shoots of Opuntia Blakeana, a prickly-pear cactus of the southwest. 2. The flat spiny joints of the normal plant, when carried into the dark chamber, produced roundish, light green, elongated, etiolated shoots which differed remarkably in form and structure from those of the normal plant, and which exhibited structural changes when transplanted in an outdoor environment that brought them to resemble the normal shoot. 3. The etiolated shoots lacked a cuticle, developed papillate structures and stomata abnormal in form and position, and lacked the cortical differentiation so characteristic of the normal shoot. 4. The etiolated-greened shoots lost water rapidly at first. Their air spaces increased rapidly by active intercellular splitting of walls and by the collapse and death of cells; then a cuticle appeared; cortical cells elongated, forming palisade tissue; and in other respects the shoots approached the normal ones in structure.