CACTACEA, SILVA OF NORTH AMERICA. 9 
OPUNTIA. 
FLowers perfect ; calyx-lobes numerous, imbricated in many series; corolla rotate ; 
petals numerous, spreading; stamens indefinite, inserted on the base of the petals; 
ovary one-celled, many-ovuled. Fruit baccate. Branches tuberculate, articulate, 
compressed, subcylindrical, or clavate. Leaves scale-like, caducous. 
Opuntia, Adanson, Fam. Pl. ii. 243 (1763). — Zucearini, 
Abhand. Akad. Minch. ii. 687. — Meissner, Gen. 128. — 
Endlicher, Gen. 945. — Engelmann, Proc. Am. Acad. iii. 
289. — Bentham & Hooker, Gen. i. 851. — Baillon, Hist. 
Pi. ix. 40 (excel. sect. Nopalea).—Schumann, Engler & 
Prantl Pflanzenfam. iii. pt. vi. 199. 
Consolea, Lemaire, Rev. Hort. 1862, 174. 
Tephrocactus, Lemaire, Les Cactées, 88 (1868). 
Ficindica, St. Lager, Ann. Soc. Bot. Lyon, vii. 70 (1880). 
Trees or usually shrubs, often low and prostrate, with flattened or subcylindrical or clavate 
articulate tuberculate branches covered by a thick epidermis with small sunken stomata filled with 
copious watery juices,’ and with or without solid or tubular and reticulate woody skeletons, and thick 
and fleshy or fibrous roots. Leaves alternate, terete, subulate, small, early deciduous, bearing in their 
axils oblong or circular cushion-like areole* of chaffy or woolly scales terminal on the tubercles of the 
branches and furnished above the middle with many short slender slightly attached sharp barbed 
bristles, and toward the base with numerous stout barbed spines* surrounded in some species, except 
1 The large thin-walled parenchyma cells which form a large former. In Opuntia fulgida the spines on an areola increase in 
part of the tissue of Opuntia take up water freely when the ground 
is moist, and the young branches become saturated with juices 
and are thick, plump, and smooth. During periods of drought, 
which frequently last for months in the regions where these plants 
grow in the greatest numbers, they gradually lose their moisture 
by evaporation and become withered and wrinkled. With the 
minute caducous leaves, thick epidermis, and small sunken stomata 
of Opuntia, this process is a very slow one, and branches severed 
from the parent plant and kept in a dry atmosphere have retained 
sufficient moisture to produce roots and branches at the end of 
nearly a year. This power to retain moisture aids in the dissemi- 
' nation of the plant, for detached joints of the branches falling to 
the ground, as they often do either naturally or by being brushed 
against by cattle and other animals, retain, in periods even of the 
longest droughts, sufficient moisture to develop roots ; these anchor 
the joints to the ground and new plants begin to grow. (See Tou- 
mey, Bot. Gazette, xx. 356 [Vegetal Dissemination in the Genus 
Opuntia].) 
2 “Tn Opuntia the pulvillus (which in its lower part is the spi- 
niferous, and in its upper part the florif areola bined) is 
the same in all stages of development ; only it is smaller on the 
lower part of each joint, and bears fewer or often no spines, and 
rarely any flowers or new shoots; while the uppermost pulvilli have 
the longest and most numerous spines, and bear the flowers as well 
asthe young branches.” (Engelmann, Bot. Mex. Bound. Surv. ii. 46.) 
“The areole continue to grow year after year, at least for a 
period of several years, and each year increase in size from the 
inner margin, several new spines developing above the old ones. 
The number of spines on an areola of a first year’s joint is fairly 
constant in the same species, but a joint several years of age may 
in some species bear six or seven times as many spines as the 
numbers with succeeding years more rapidly than in Opuntia spino- 
sior. In the latter, however, they increase much more rapidly than 
in Opuntia versicolor. On this species frequently no additional spines 
are produced after the first year, and they are never produced in 
such numbers as on the two other species. In these three species, 
after several years’ growth the vegetative activity of the areole 
ceases, and they fall away with the outer scales of the bark.” 
(Toumey, in litt.) 
3 The spines of Opuntia, which are produced on most of the spe- 
cies and are usually stout and rigid, are barbed backward, and 
make these plants the most difficult and dangerous of all the Cac- 
tus family to handle, or even to approach, and render several of 
the large-growing specimens valuable for the protection of fields 
and gardens against browsing animals. The short sharp bristles 
mixed with soft scales, which cover the areole above the middle, 
are also barbed backward, and being very feebly attached come off 
with the slightest touch, penetrating the skin or adhering to the 
clothes of persons brushing by the plants. (See Engelmann, l. c. 45.) 
The spines and, in a less degree, the bristles of Opuntia and of 
many other members of the Cactus family, which often contain the 
only moisture to be found in the deserts of America, have evidently 
been developed to protect these plants against animals suffering 
from thirst, who would soon exterminate them without this protec- 
tion. They also play an import: 
part in the di of Opun- 
tias, the barbed spines attaching themselves to passing animals, who 
carry off the easily detached joints of the branches, which sooner or 
later reach the ground and often form new plants. Certain species 
with strongly developed and numerous spines and feebly attached 
joints rarely produce seeds and appear to depend almost entirely 
on this method of propagation. (Teste Toumey, in litt. See Ganong, 
Bot. Glazette, xx. 133.) 
