CoIvD-Resistance in Spineless Cacti 



127 



Fig. 3. — Cross-section of a piece of joint of Opunlia 

 sp. Burbank Special, about two years old. Note the 

 relatively thin integument. (Highly magnified). 



Fig. 4. — Cross-section of a piece of joint of Opun- 

 tia Ellisiana about two years old. Note the thick 

 integument. (Highly magnified). 



3. Opuntia sp. Burbank Special. The integument of this species 

 is thin. The cuticle is 5 to 8 ji. thick, the crystal-bearing layer 30 to 

 38 [K, and the thick-celled layer 70 to 87 [i. This species is not 

 hardy and was killed at a temperature of — 8° C. (17.6° F.). 



4. 0. Ellisiana has, Uke 0. castillae, a thick cuticle of 12 to 15 [x, 

 a crystal-bearing layer of 25 to 35 [x, and the next layer of 75 to 

 130 [I. This species is quite hardy; it is said to be resistant to tern- 



