380 TRANS. ST. LOUIS ACAD. SCIENCE. 



thirds up. DeCandolle has observed the same in the Cork-oak 

 of Europe and in some Mexican White oaks. The Black-oaks 

 with annual fructification have these ovules always suspended 

 near the tip of the seed, and are in this respect undistinguishable 

 from the regularly biennial Black-oaks. 



It is well known that in the southeastern Live-oak both cotyle- 

 dons are united into one mass — a singular but isolated fact which 

 has no systematic significance. 



In the foregoing pages I have purposely left aside the very 

 peculiar Californian ^. densi/tora, which is in every respect diff- 

 erent from the other oaks, and thus far the sole representative of 

 a peculiar group named by DeCandolle A7idrogyne. In many 

 respects it is more a chestnut than an oak, for it has, just like the 

 chestnuts, the same dense-flowered, erect male spikes, 10 stamens 

 to each flower, very small anthers on long filiform filaments, with 

 very small pollen-grains (0.017 mm. in diam., not much more 

 than half as large as in other oaks), and in the female flowers 

 slender, terete, pointed stigmas, grooved above. In place of the 

 spiny involucre of the chestnut our plant has a spiny cup. and 

 is thus made an oak and not a chestnut. The maturation is 

 biennial. The shell of the nut is thicker and harder than in any 

 other of our oaks, the inside thickly tomentose, and the abortive 

 ovules are found near the top of the seed. The wood is brittle 

 and worthless. 



It results from these investigations that our oaks, leaving again 

 aside the one last mentioned, arrange themselves into two great 

 groups, often alluded to above as the White-oaks and the Black- 

 oaks. 



The White-oaks are characterized by paler, often scaly, bark, 

 tougher and denser wood, and sessile or subsessile stigmas, and 

 bear the abortive ovules at the base or rarely on the side of the 

 perfect seed. Besides this, the leaves and their lobes or teeth are 

 obtuse, never bristle-pointed, though sometimes spinous-tipped : 

 their stamens are more numerous, the scales of the cup more or 

 less knobby at base, the inner surface of the nut glabrous or 

 (rarely) pubescent ; the fruit generally matures in the first year. 



The Black-oaks have dark, furrowed bark, brittle and porous 



