256 
A VENA 
sativa L., the cultivated oat, is perhaps derived from A.fatua L. It 
is cultivated in Eur. to 69 4 ° N. and forms the staple of the food of a 
large population. [See De Candolle’s Orig . of Cult . Pits. p. 373-] 
The 2 — 6-flowered spikelets form a loose panicle. The paleae are 
awned, the awn of the inf. palea being usually twisted and hygro- 
scopic. In A . sterilis L. the awns cross, and when wetted try to 
uncurl and thus press on one another till a sort of explosion occurs 
jerking away the fruits. 
Averrhoa Linn. Oxalidaceao. 3 or 4 sp. trop. As. (?). A. Bilimbi 
L., the Blimbing, is cultivated for its fruit, which is borne on the 
older stems (p. 156). 
Avicennia Linn. Verbenaceae (vn). 3 sp. trop., forming one of the 
constituents of the mangrove-vegetation (p. 191). They have the same 
vivipary, habit &c., and show aerial roots projecting upwards out of 
the mud like those of Sonneratia. 
Azalea Linn. Now united to Rhododendron Linn., from the type form 
of which it is chiefly distinguished by its 5 sta. and annual leaves. For 
A. procumbens L. (Brit.) see Loiseleuria. 
Azara Ruiz et Pav. Flacourtiaceae. 22 sp. Mex. and S. Am., chiefly 
Chili. Shrubs with alt. leaves; one stipule is frequently almost as 
large as the leaf to which it belongs, giving the appearance of a pair 
of leaves not opposite to one another. The flr. is apetalous and the 
outer sta. often without anthers. 
Azima Lam. Salvadoraceae. 2 sp. trop., Afr., As., Polyn. In the 
leaf axils are thorns (the leaves of an undeveloped shoot, cf. Cac- 
taceae). Fir. polypetalous. 
Azolla Lam. Salviniaceae. 4 sp. trop. and sub-trop. The general 
structure is like that of Salvinia. Two leaves are formed at each 
node, from the dorsal half of a segment of the apical cell; from the 
ventral half are formed roots and branches, but not at every node. 
The leaves are all alike ; each is bilobed and has a small cavity near 
the base, opening to the outside by a small pore, and inhabited by 
the Alga Anabaena. The roots hang freely down in the water; 
usually the root cap is thrown off after a short time and the root 
comes almost exactly to resemble the submerged leaf of Salvinia. 
The sporocarps are formed in pairs (4 in A. nilotica ) on the ventral 
lobes of the first leaves of the branches. Each contains one sorus. 
The microspores are joined together into several masses in each 
sporangium by the hardened frothy mucilage (epispore, cf. Salvinia). 
Each of these niassulae has its outer surface provided with curious 
barbed hairs ( glochidia ), and escapes from the sporangium on its own 
account. The megasporangium contains one spore. It sinks to the 
bottom and at length decay of the indusium frees the spore and it ger- 
minates, giving rise to a female prothallus which floats about on the 
water and may be anchored to a floating massula by the barbs. 
Azorella Lam. Umbelliferae (1). 35 sp. S. temp. Densely tufted 
