OF ARTS AND SCIENCES. 305 



two genera, of which the leading one is the strongly quincuncial calyx, 

 and not to force them into an order, nor into a cohort, of which a val- 

 vate calyx is an essential and substantially an unvaried character. As 

 a small order, it takes a comfortable position between the Guttiferal 

 and Malval cohorts in the Genera Plantarum, connecting the two, and 

 with no technical character alien to the former. 



TiliacecB. 



TILIA. Although our species are not absolutely limited, it seems 

 necessary to restore 2\ pubescens to specific rank, and so to recognize 

 three species, viz. : — 



T. Americana, L., with ample leaves essentially glabrous, thickish 

 and firm, green on both faces, the upper lucid; floral bract usually 

 tapering into a stalked base (except the uppermost) ; fruit ovoid, 

 usually lightly costate. 



T. PUBESCENS, Ait., with smaller and mostly thinner leaves, dis- 

 tinctly pubescent beneath, yet often glabrate in age : floral bract usu- 

 ally rounded at base and sessile or hardly stalked : fruit globular. I 

 do not adopt the older name of 2\ Garoliniana, Mill. Diet. ; for the 

 original character, as well as that of Marshall and of Wangenheim, 

 points to T. Americana rather than to T. pubescens. Probably to 

 that species also belongs the T. pubescens of the Nouveau Duhamel. — 

 The var. leptophylla. Vent., is very well marked by its larger and 

 thin leaves. It is hardly possible to combine this form with T, Ameri- 

 cana, and its habitat is much more southern. 



T. heterophylla. Vent., the T. alba of Michx., but not of Alton, 

 is well marked by its ample leaves of ovate outline (not rounded as in 

 the true T. alba of S. E. Europe), whitish or silvery beneath ; floral 

 bract tapering to a very short-stalked or sessile base, usually elongated, 

 and the peduncles still longer ; the fruit globular. It strictly belongs 

 to the Alleghany region, from Southern Pennsylvania to Florida. 

 The original reference of Alton's T. alba to America was corrected 

 in the second edition of the Hortus Kewensis. But, having been cop- 

 ied by Ventenat, under his T. rotundifoUa, the mistake has been kept 

 up by Bayer in his Monograph, who places it under his T. hetero- 

 phylla-nigra, and has two forms from Kentucky, both undoubtedly 

 T. heterophylla. 



T. Mexicana, Schlecht., which Bayer makes a variety of T. pubes- 

 cens, is probably a good species. The floral bracts taper to a slender- 

 stalked base. 



VOL. XXII. (N. S. XIV.) 20 



