308 BOTANICAL GAZETTE. | Nov., 
strengthening cells in small bundles eeberntec by the rows of sto- 
mata, much more numerous and larger in the angles; generally 
present in the fibro-vascular region : arses 1-23 in. long. 
In the mountains from Pennsylvania to Tennessee. 
++ ++ Nostrengthening cells in fibro-vascular region, nor about the ducts. 
== Leaves in threes. 
31. P. tubereulata Gordon. Thin-walled cells smaller than 
epidermal: strengthening cells in one or two rows, larger than 
3 epidermal cells ; rarely some about ducts and on dorsal side 
bro-vascular ts ducts 2 to 5, small (.020-.030 mm.), 
an with several internal. 
Throughout the western Scie systems. 
23. P. Teda L., and 
26. P. insignis Doug]. may be looked for here. 
= = Leaves in pairs. 
32. P. inops Ait. Epidermal and strengthening cells about 
the same size and quite small, the latter in a single layer: lines 
of stomata quite numerous : ducts occasionally internal: “fibro- 
vascular bundles often wiaelf separated: leaves 13-3 in. long. 
Along the coast from New York to S. Carolina, westward through Ken- 
tucky to Indiana. 
3. P. elausa Vasey. Lines of stomata 10-20: strengthening 
eells ote pais wanting, or with a few scattered peripheral 
ones: ducts mostly two, one of which is occasionally internal, 
bi Mal but little in size- (.030-.035 mm): leaves but half as 
wide (1 mm.) and longer than the last. 
Psia 
34. P. mitis Michx. But one layer of strengthening — 
which are little smaller than the epidermal : ducts st ual 
-030 mm 2. offen as many as six: leaves 3-5 in. long, not twi ice as 
wide as thie 
New York to Florida, westward to Texas and Kansas. 
35. P. glabra Walt. Ducts rather large (.050-.060 mm.) for 
the group, ewes than in the last, mostly 2 or 3, ec gee me 
one of them internal: leaves 3-4 in. long, twice as wide as t 
South Carolina to Florida and through the Gulf States to Louisiana. 
36. P. Banksiana Lamb. Cells of thin-walled layer smaller 
