i92o] BROWN— STOM ATA 301 







erm 



but two general physiological regions could be recognized: an 

 outer leucoplast-containing one 3-5 layers of cells thick, and an 

 inner starch-containing one reaching to the stele (fig. 13). The 

 leucoplasts of the outer cortical region were actively budding, 

 like the chloroplasts of the epidermis, but were mostly smaller, 

 and the smallest sizes increased in number in proportion to the 

 distance from the surface of the shoot. Air spaces were much less 



normal cortex, and were often formed 



mally 



Etiolated-greened shoot 



Etiolated shoots placed in the laboratory windows and those 

 transferred to the open presented similar changes in structure, 

 but the changes were more rapid in the latter environment. Decor- 

 tication removed the abnormal stoma ta with the papillae, and 

 none reappeared (figs. 15, 29). Chloroplasts quickly disappeared 

 from the epidermal cells. The whole shoot presented a shrunken 

 appearance, due not only directly to the water loss from the 

 almost unprotected tissues, but also to the actual death of many 

 of the cells in the outer cortex (figs. 15, 16), a process by which 

 air cavities were quickly enlarged. As cutinization progressed in 

 the epidermis, and the turgidity of the cortical cells gradually 

 became restored, the whole topography of the cross-section 

 changed, for palisade tissue had appeared (fig. 12). Intracellular 

 changes also occurred in the cortical cells. The chloroplasts were 

 reduced in number as compared with the leucoplasts in the outer 

 cortex of the etiolated shoot. They were regularly rounded in 

 form and were present in cells as deep as the stelar region (fig. 12). 

 They were necessarily confined to the peripheral region of the 

 cell because of extensive vacuolization, and were found on end 

 walls and lateral walls. 



The new branches that appeared from the buds that had 

 formed on the etiolated shoots before their removal to the light 

 were larger, both in breadth and thickness, than the branches of 

 the etiolated stems; and spines, glochids, and bristles were more 

 like those of the normal plant in size and general appearance. 





