Vol. 45 - No. 9 
BULLETIN 
OF THE 
TORREY BOTANICAL CLUB 
SEPTEMBER, 1918 
Wound periderm in certain cacti 
Mary WOoTHERSPOON COUTANT 
(WITH PLATE 9 AND THREE TEXT FIGURES) 
NORMAL TISSUE 
The two cacti upon which the work of this paper is based are 
Opuntia versicolor Engelmann and O. discata Griffiths. These 
are jointed, branching forms, characteristic of the flora in the 
vicinity of Tucson, Arizona. Morphologically they differ in that 
the joints of the O. versicolor are composed of fluted cylinders, 
while those of the O. discata are more or less disc-shaped. 
Necessarily, a cross section of the former presents the appearance 
of a circle with an undulating margin, while one of the latter is 
more of an elongated ellipse. Anatomically considered, they are 
identical in all essentials. There is (1) a distinct pith in the 
center, bounded (2) by a ring of bundles equidistant from the 
exterior; outward from the bundles (3) a ring of cortical tissue, 
which extends to the (4) hypoderm, outside of which is the (5) 
epidermis. Subepidermally, in plants several years old, normal 
periderm occasionally, but not typically, forms in isolated areas. 
Schleiden (3), in his early work on the cacti, describes fairly 
accurately several forms, which, however, do not include either 
O. versicolor or O. discata. 
A further discussion of the tissues in their normal condition is 
prerequisite to a complete understanding of their behavior as a 
result of wounding. 
[The BULLETIN for August (45: 309-352) was issued September 9, 1918.] 
353 
