ACA 



ACA 



thistle-leaved acanthus was found by 

 Sparrman at the Cape of Good Hope, and 

 has many leaves, proceeding immediately 

 from the root, resembling those of the 

 thistle. 3. The prickly acanthus grows 

 wild in Italy and Provence, and flowers 

 from July to September. Its leaves are 

 divided into segments, terminated with a 

 sharp spine, which renders this plant trou- 

 blesome to those who handle it. 4. The 

 acanthus of Dioscorides, as Linnaeus sup- 

 poses it to be, grows naturally in the East, 

 on Lebanon, Sic. 5. The holly-leaved 

 acanthus is an evergreen shrub, about 

 four feet high, and separating into many 

 branches, with leaves resembling those 

 of the common holly, and bearing white 

 flowers, similar to those of the common 

 acanthus, but smaller. 6, 7, 8, 9. These 

 species, viz. the entire-leaved, procum- 

 bent, forked, and Cape acanthi, are na- 

 tives of the Cape of Good Hope. 10. The 

 Madras acanthus is a native of the East 

 Indies. 



The smooth and prickly acanthi are pe- 

 rennial plants, and may be propagated ei- 

 ther by seeds, which should be sown in a 

 light dry soil towards the end of March, 

 and left to grow, about six inches asunder, 

 till autumn, when they should be trans- 

 planted where they are to remain : or by 

 roots, which may be planted either in 

 spring or autumn for the third sort; but the 

 others must only be removed in the spring, 

 because, if they are transplanted in au- 

 tumn, they may be in danger of being de- 

 stroyed by a cold winter. These plants 

 take deep roots, and when they are once 

 established in a garden, they cannot be 

 easily eradicated. The 5th and 10th spe- 

 cies are too tender to thrive out of a stove 

 in England, and cannot be propagated, 

 except by seeds, which do not ripen in 

 Europe. The other sorts must be treat- 

 ed in the same manner with Cape plants. 



ACANTHUS, in architecture, an orna- 

 ment representing the leaves of the herb 

 acanthus, and used in the capitals of the 

 Corinthian and Composite orders. See 

 ARCHITECTURE. 



ACARNA, in botany, a genus belong- 

 ing to the Syngenesia JEqualis class and 

 order: receptacle chaffy: down feathery: 

 calyx imbricate, invested with scales, co- 

 rol. floscular. There are seven species. 



ACARUS, the tick or mite, in natural 

 history, so called, because it is deemed so 

 small that it cannot be. cut, is a genus of 

 insects belonging to the order of Aptera, 

 in the Linnaean system. Gmelin, in the 

 last edition of Linnseus's system, has 

 eighty-two species ; of which, some are 



inhabitants of the earth, others of water ; 

 some live on trees and plants, other* 

 among stones, and others on the bodies 

 of other animals, and even under their 

 skin. The generic character is, legs eight; 

 eyes two, situated on each side the head ; 

 feelers two, jointed ; egg-shaped. The 

 most familiar species are, 1. the A. siro, 

 or common cheese-mite, which is a fa- 

 vourite subject for microscopic observa- 

 tions. This insect is covered with hairs 

 or bristles, which resemble in their struc- 

 ture the awns of barley, being barbed on 

 each side with numerous sharp-pointed 

 processes. The mite is oviparous : from 

 the eggs proceed the young animals, re- 

 sembling the parents in all respects, ex- 

 cept in the number of legs, which at first 

 amount only to six, the pair from the head 

 not making their appearance till after 

 casting the'ir first skin. The eggs in warm 

 weather hatch in about a week, and the 

 young animal may sometimes be seen for 

 a day together struggling to get rid of its 

 egg-shell. The mite is a very voracious 

 animal, feasting equally upon animal and 

 vegetable substances. It is also extremely 

 tenacious of life ; for, upon the authority 

 of Leewenhoek, though highly discredit- 

 able to his sense of humanity, we are as- 

 suredthat a mite lived eleven weeks glued 

 to a pin, in order for him to make observa- 

 tions on. 2. The A. exculcerans, or itch 

 mite, is a species of considerable curiosity, 

 on account of the structure of its limbs : it 

 is slightly rounded, and of a flattened 

 shape, with the thighs of the two upper 

 pair of legs extremely thick and short : 

 the two lower pair of legs have thick 

 thighs, proceeding from a very slender 

 base, and are extended into a long, stout, 

 curved, and sharp-pointed bristle. Dr. 

 Bononio, an Italian physician, was the 

 first who contended that the itch was oc- 

 casioned by this insect, an account of 

 which may be found in the Philosophical 

 Transactions, No. 283. Dr. Baker is in- 

 clined to think that it constitutes the /wo- 

 ra, a species of itch distinct from others 

 confounded with it. 3. A. autumnalis, or 

 harvest-bug, of a bright red colour, with 

 the abdomen beset on its hind part with 

 numerous white bristles. It attaches itself 

 to the skin, and is with difficulty disen- 

 gaged. On the part where it fixes, it 

 causes a tumour, about the size of a small 

 bead, accompanied by a severe itching. 

 The tick is of this species, which is to be 

 found on dogs and other animals. Many 

 of the acari attach themselves to insect* 

 of a larger kind, and hence they take their 

 names, as A. coleopterous, found on the' 



