ROBINSON: CONTRIBUTIONS FROM GRAY HERBARIUM. 265 
From P. islandicum, Meisner, to which P. caurianwm shows also 
much affinity, it may be distinguished by its more slender stems, 
smaller flowers, and erubescent calyx with a more spreading limb. 
The achenes are also shorter. 
Dimorpuism tN PoLyGoNuUM LONGISTYLUM. An examination of 
typical material of P. longistylum, Small, with its long-exserted 
style-branches and short included stamens immediately suggested 
that this was merely one form of a dimorphic species, and that the 
other form would be found to have a complementary flower with 
proportionately short style-branches and long stamens. Search in 
the related material in the Gray herbarium has shown this to be the 
case. The short-styled form is represented by specimens from 
Dunklin county, Missouri, Bush, no. 117A; western Kansas, Mee- 
han; Kingfisher county, Oklahoma, LZ. A. Blankinship; Houston 
and Lynchburg, Texas, Zindheimer; and Southerland Springs, 
Texas, Dr. Palmer, no. 1188. These specimens have been vari- 
ously distributed under the names of P. pennsylvanicum and P. 
mexicanum. During anthesis the length of the style from the sum- 
mit of the ovary to the tip of the stigma is 1.2 mm., while the fila- 
ments are 3 mm. in length. In the long-styled form these lengths 
are just reversed. It may be noted that the stigmas are subglobose 
in the short-styled form, but clavate in the long-styled. In the light 
of the dimorphic character of the flowers the specific name seems 
unhappily chosen. In the habitally similar P. pennsylvanicum, L., 
anthers and stigmas attain at anthesis essentially the same height 
and no dimorphism can be detected 
5. New SperRMATOPHYTES OF Merxico AND CENTRAL AMERICA. 
Hechtia tehuacana, spec. nov. Robusta; foliis lineari-lanceo- 
latis a basi ampliata ad apicem rigidum gradatim angustatis argen- 
teis 4 dm. longis, margine aculeis atrobrunneis lucidis tenuibus rigi- 
dis faleato-curvatis 4-5 mm. longis armata; scapo robusto, ramulis 
inflorescentiae ¢ in axillis bractearum magnarum ovatarum acumi- 
natarum glabrescentium ad 3-4 fasciculatim orientibus 4-8 cm. 
longis curvato-adscendentibus subdense fioriferis; fioribus viride 
lutescentibus subsessilibus 4-5 mm. longis; bracteolis late ovatis 
acutiusculis glabris 2-2.5 mm. longis; sepalis ovatis vel suborbicular- 
