228 
AGLAONEMA 
Aglaonema Schott. Araceae (v). 10 sp. E. Ind. There are several infl. 
forming a sympodium. Fir. monoecious, naked. 
Agonis Lindl. Myrtaceae (2). 13 sp. Austr. 
Agrimonia Toum. Rosaceae (in. 9). 10 sp. N. temp. A. Eupatoria 
L. and A. odorata Mill, (agrimony) in Brit. The recept. encloses 
the two achenes in frt. and is covered with hooks for animal carnage. 
Agropyron J. Gaert. Gramineae (xn). 32 sp. temp. A . canmum 
Beauv. and A. repens Beauv. occur in Brit. The latter is the twitch 
or couch grass, a very troublesome weed in agriculture. It has a long 
rhizome, rooting at the nodes. If broken up by plough or harrow 
each node gives rise to a new plant, hence it is very hard to eradicate. 
Agrostemma Linn. =* Lychnis L. 
Agrostis Linn. Gramineae (vm). 100 sp. chiefly N. temp. 4 Brit, sp., 
including A. alba L. the white Bent- or Fiorin-grass, a valuable pasture 
grass with a creeping stem that roots at the nodes. 
Ailanthus Desf. Simarubaceae. 4 sp. Ind., Chi., Austr. A. glandu- 
losa Desf., the tree of heaven, is a favourite in parks. Absciss layers 
are formed at the base of the leaflets as well as of the main petiole ; the 
former usually drop first. Buds are formed on the roots (?). 
Ainsliaea DC. Compositae (xii). 16 sp. Ind. to Japan. 
Ainsworthia Boiss. = Tordylium L. 
Aira Linn. Gramineae (ix). n sp. chiefly Eur., Afr. 2 sp. in Brit, 
(for A . caespitosa L. and A . flexuosa L. of Brit, flora, see Des- 
champsia, and for A . canescens L. see Corynephorus). 
Aizoaceae ofBenth.-Hook.). Dicotyledons (Archichl. Centro- 
spermae). 18 gen. with 420 sp. chiefly S. Afr. They are nearly 
allied to the other Centrospermae, but have been placed in various 
other relationships by other authors (near Cactaceae by B. and H.). 
Xerophytic herbs with opp. or alt. exstip. leaves, often fleshy, and 
with cymes of flowers. The anatomy is of interest (see Nat. PJl .). 
The typical formula, according to Pax, is P 5 (odd leaf posterior) ; 
A 5; G(3), 3-locular with 00 ovules in each. In the androeceum, 
dedoublement is very common, and in these cases the outer sta. 
are frequently represented by petaloid staminodes (e.g. Mesembry- 
anthemum). The ovary is usually sup. with axile plac. but in 
M. it is inf., multiloc. with parietal plac., a very unusual feature, 
brought about during development (see M.). Fruit usually a cap- 
sule ; seed albuminous with curved embryo. 
Classification and chief genera (after Pax): 
I. MOLLUGINOIDEAE (perianth deeply 5-lobedj ‘petals* 
or not: ov. sup.) : Mollugo, Orygia. 
II. FICOIDEAE (perianth tubular) : 
1. Sesuvieae (ov. sup. ; caps, with lid) : Sesuvium, Trianthema. 
2. Aizoeae (do.; caps, splitting): Galenia, Aizoon. 
3. Mesembryantheineae (ov. inf.) : Tetragonia, Mesembry- 
anthemum. 
