860 TREES OP NORTH AMERICA 



at apex; pericarp thin, light green, villose-pubescent on the outer surface, longitudinally 

 veined on the inner surface, opening by the ventral suture and displaying the embryo en- 

 larging before separating from the branch, ultimately 2-valved. Seed naked, without al- 

 bumen; embryo filling the cavity of the fruit, light green; cotyledons thick and fleshy, 

 broader than long, slightly pointed, deeply cordate at base, unequal, conduplicate; radicle 

 elongated, clavate, retrorsely hirsute, inferior, descending obliquely and included between 

 the lobes of the cotyledons slightly attached near the apex in the bottom of the capsule to 

 the withered columella by a minute papillose point; plumule hairy. 



Avicennia with three species is widely distributed on maritime shores of the tropics of the 

 two worlds, with one species reaching those of the southern United States. Avicennia pro- 

 duces hard strong wood. The bark is rich in tannic acid, and is used for tanning leather. 

 The chief value of these trees is in their ability to live on low tidal shores by the structure 

 of the embryo, which is growing and ready to take root as soon as it falls into the soft mud, 

 and in the long horizontal roots furnished with short vertical fleshy leafless branches or 

 aerating roots, forming a close network which holds the soil together and prevents it from 

 being washed away by outflowing tides, and extends the growth of the tree by numerous 

 stems which soon form dense thickets. 



The generic name is in honor of the illustrious physician of the Orient, Avicenna of 

 Bokhara (980-1036). 



1. Avicennia nitida Jacq. Black Mangrove. 



Leaves oblong or lanceolate-elliptic, rounded or acute at apex and gradually narrowed 

 at base, dark green and often lustrous above, hoary-tomentulose below, 2'-3' long and '- 

 1^' wide, with slightly thickened re volute margins, a broad midrib thickened and grooved 



Fig. 765 



toward the base on the upper side, and oblique primary veins arcuate and joined close to 

 the margins, conspicuous on the 2 surfaces, and connected by prominent reticulate veinlets; 

 appearing irregularly and falling early in their second season; petioles broad, channeled, 

 enlarged at base, and about \' in length. Flowers produced continuously throughout the 

 year, their bracts and bractlets nearly \' long, coated with pale or slightly rufous pubes- 

 cence and about as long as the lobes of the calyx, in few-flowered short spikes on stout 4- 

 angled canescent peduncles \'-\\' in length, the lateral peduncles of the ternate terminal 

 cluster subtended by oblong acute bracts %' long; corolla \' across the expanded slightly 

 tomentose lobes, and nearly closed in the throat. Fruit \'-\\' long and f'-l' wide. 



A tree, occasionally 60-70 high, with a short trunk rarely 2 in diameter, spreading 

 branches forming a broad round-topped head, and branchlets at first slightly angled, coated 



