ENGELMANN OAKS OF THE UNITED STATES. 397 



little known and often doubted species. It grows on the poorest sand 

 ridges near Bluffton, together with Pinus australis, very rare there, 

 but apparently extending along the coast to Florida. It makes an ever- 

 green shrub from ih~-, usually 4-5. and up to S feet high. Leaves 

 rounded ovate, cordate, obtuse, or sometimes acute at base, obtuse and in 

 youth bristle-pointed at tip, revolute on the margin, thick and leathery, 

 persisting 15-18 months. Leaves vary sometimes to broadly obovate, or 

 are rarely, in young shoots, sinuate-angled; they are usually i-i£ or even 

 2 inches long, but in vigorous ground shoots have been found 2i and 3 

 inches in length by 2 in width. The young leaves are densely covered 

 with a rusty, clammy scurf of articulated hair, which after a month or so 

 disappears, leaving a glossy surface. Vernation imbricate ; youngest leaves 

 flat with recurved margins. Aments about iA inches long with stellate- 

 canescent rhachis, 5 oval pubescent calyx lobes, and a few (mostly only 

 2-3) small cuspidate anthers. Fruit sessile or usually short peduncled, 

 single or in twos; cup very shallow, about 6 lines wide, with ovate-trian- 

 gular obtuse scales; gland ovate or subglobose, 5 or 6 lines long, covered 

 by the cup for \ or J of its length. — Jg. myrtifolia, Willd., Nuttall, Pursh, 

 Elliott, only the first two of which seem to have seen sterile specimens; 

 flower and fruit had been unknown. — J9. Phcllos var. arenaria, Chapm. ; 

 ^). aquatica var. myrtifolia, A. DC. 



Hybrid Oaks. 



The question of hybridity in plants is in every case difficult to 

 solve where its usual character, the sterility* of the hybrid, fails 

 us, and where we have nothing to rely on but the rarity and indi- 

 viduality of a form that seems to stand intermediate between two 

 well established species which occur in its neighborhood, and 

 which could be considered its parents. 



This is just the case in oaks. All the supposed hybrids are 

 abundantly fertile, and those of their acorns which have been 



* On ihe muddy banks of the Mississippi near this city, where several species of Nas- 

 turtium (palustre, obtusum, sessiliflomni, and sinuatuui )'a.re abundant, two hybrids occur 

 among them which will illustrate the different sexual qualities which hybrids may possess. 

 The first, an offspring of palustre and simiatum, is a normal hybrid with small anthers and 

 abortive, shrivelled pollen grains, with unimpregnable though apparently well- formed 

 ovules, and small and absolutely sterile pods. It is perennial Uke'siuuatum, and erect like 

 palustre, abundant flowers of intermediate size, in long, virgate racemes, and, singularly 

 enough, with uncommonly large stigmas. The other, a hybrid between palustre and obtu- 

 sum, on the contrary, produces i^ood pollen and is quite fertile, so that it might be ques- 

 tionable whether it really is a hybrid; and indeed it has all along been considered a form of 

 obtusum until Mr. Eggert pointed out its intermediate character. The true obtusum is 

 always prostrate and small (branches not more than 6 inches bong), has minute whitish 

 flowers, petals only half as long as sepals, small orbicular anthers, and elongated, suberect 

 pods on very short pedicels. N. palustre is erect, has large oblong anthers and shorter 

 patulous, long-pedicelled pods. The cross occurs in all forms, from the small and pros- 

 trate to the tall and erect one, often as if struggling between an erect and a decumbent 

 habit, with some branches in one, others in another direction; the yellow petals aie longer 

 than in obtusum but much smaller than in palustre, anthers as in the former; pods shorter 

 than in obtusum, on longer, patulous pedicels. 



