ROBINSON: CONTRIBUTIONS FROM GRAY HERBARIUM. 2()5 
From P. islandicum , Meisner, to which P. caurianum shows also 
much affinity, it may be distinguished by its more slender stems, 
smaller dowers, and erubescent calyx with a more spreading limb. 
The achenes are also shorter. 
Dimorphism in Polygonum 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 dower 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 ; Kingdsher county, Oklahoma, L. A. Blankinsliip ; Houston 
and Lynchburg, Texas, Lindheimer ; 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 dowers the specidc name seems 
unhappily chos'en. 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 Spermatophytes of Mexico 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 falcato-curvatis 4-5 mm. longis armata; scapo robusto, ramulis 
indorescentiae £ axillis bractearum magnarum ovatarum acumi- 
natarum glabrescentium ad 3-4 fasciculatim orientibus 4-8 cm. 
longis curvato-adscendentibus subdense doriferis; doribus viride 
lutescentibus subsessilibus 4-5 mm. longis ; bracteolis late ovatis 
acutiusculis glabris 2-2.5 mm. longis; sepalis ovatis vel suborbicular- 
