28 o 
C. AC ALIA 
Cacalia Linn. = Senecio Toum. (usually same spec, names). 
Caccinia Savi. Boraginaceae (iv. i). 7 sp. W. and Cent. As. 
Cachrys Linn. Umbelliferae (6). 8 sp. Medit., W. and Cent. As. 
Cactaceae. Dicotyledons (Archichl. Opuntiales). 15 gen. with abt. 
900 sp. The order is chiefly localised in the dry regions of trop. 
Am., but it spreads to a considerable distance N. and S. ( Opuntia 
missouriensis is found as far as 59 0 N.). The cacti are able to stand 
winter frost very well (as the splendid open-air collection at Cambridge 
testifies) and so are found far up the mountains (to 12000 ft. and even 
higher). Even in the damp forest regions some sp. appear as epi- 
phytes. The only representative of the order in the Old World is 
Rhipsalis, found in Afr., Mauritius &c., but several sp. of Opuntia &c. 
are now naturalised in S. Afr., Austr., &c. and are becoming as trouble- 
some as the thistles of the Pampas or Elodea in Europe. 
The C. are xerophytes of the most pronounced type, exhibiting 
not merely reduction of the transpiring surface, but also storage of 
water, often in very great quantity. The vegetative organs show 
great variety of type ; the C. afford an interesting case of a family in 
which the classification is better based upon them than upon the 
reproductive organs (see below). The root is generally long and 
well-developed (in cultivation it is liable to decay). The stem is 
fleshy, of various shapes, rarely bearing green leaves, and usually 
provided with sharp barbed thorns, which give a most efficient pro- 
tection against animals. We shall now consider briefly some of the 
more important types of shoot found in C. (refer to genera for further 
details). The nearest approach to the ordinary plant-type is found in 
Pereskia, which has large green leaves, somewhat fleshy, in whose 
axils are groups of thorns mixed with hairs ; the space occupied by 
these is termed the areole . About the morphology of the spines there 
has been much dispute; most authors regard them as representing 
the leaves of the axillary shoot, whose stem is undeveloped, but there 
is also good evidence in favour of the view that they are ‘emergences’ 
(p. 1 14). In some genera they are provided with barbs. The next 
stage is found in Opuntia, where the stem has taken over the water- 
storing and assimilating functions, but still bears leaves ; in some sp. 
these aid the stem functions throughout life, but in most they fall off 
very early, and the stem is usually flattened to expose more surface to 
air and light. Then we come to Leuchtenbergia, which has an aloe- 
like habit with the areoles on the tips of the apparent leaves; the fir. 
arises either in the axil of the ‘leaf’ or on the areole. Development 
shows that the apparent leaf is really a compound structure. The 
bud stands, not exactly in the axil, but on the base of the leaf, and 
the two grow out together to form a leaf-cushion or mammilla , at the 
outer end of which is the growing point and the rest of the leaf itself; 
the latter is represented by a small scale (often microscopic) and the 
former gives rise to the thorns &c. on the areole. The same pheno- 
