

BCORTICAL FORMATION AND ABNORMAL DEVELOP- 

 MENT OF STOMATA IN ETIOLATED SHOOTS OF 



OPUNTIA BLAKEANA 



J. G. Brown 



(with PLATES XXVII-XXX AND one figure) 



Introduction 



Although experiments in the etiolation of plants date back to 



mor 



the activities of Charles Bonnet, their contributions to 

 phological botany have largely been incidental to the prosecution 

 of physiological studies, and therefore extensive only as regards 



number 



of species subjected to investigation. Even up to the 

 present century, literature contains little more than observations 

 on gross structural changes induced or accompanying etiolation, 

 such as the elongation of internodes and peduncles, the dwarfing 



tissues. 



elopment 



material 



in this paper adds several new and important facts. Since other 

 investigators (4) have given reviews of the literature on etiolation, 

 the writer will pass directly to his own studies. 





Material 



Opuntia Blakeana is a common, low-spreading, prickly-pear 

 cactus on the mesas of southern Arizona, having joints 10 cm. in 



in thickness ffier. 1). The 



cm 



length, 9 cm. in breadth, and 1-2 

 joints exhibit purplish areoles. Each areole near the margin and 

 in the middle region of a joint bears one or two brown spines 

 1-3 cm. long. On the basal portion of a joint and on the lowest 

 joints of the plant, areoles are often without spines. In addition 

 to the spines, areoles frequently bear glochids about half the 

 length of the spines, which are especially numerous near the apex 

 of the joints. Both spines and glochids are of the usual barbed 

 type found in cacti. Many bristles about 4 mm. in length, con- 

 sisting of a single row of cells, are inserted near the bases of the 



295] 



[Botanical Gazette, vol. 70 







