ne, A ee < gern emer ae 
49 
My Opuntia frutescens (Plant. Lindh. 1. c. p. 245.) which had 
been collected by Mr. Lindheimer along the Colorado and 
Guadaloupe rivers, in Texas, was also found south of Chihuahua 
by Dr. Wislizenus, and again along the route near Parras, and 
below Monterey. The suggestion made in the Plant. Lindh., 
that it may be a southern variety of O. fragilis of the Upper 
Missouri, has proved to be erroneous, as they belong to quite 
distinct sections of the genus Opuntia; O. frutescens, together 
with O. vaginata, is one of the Opuntia cylindracee graciliores, 
and is apparently nearly related to O. /eptocaulis DC., but is 
easily distinguished by its strong, white, single spines, while 
the latter has three short blackish bristles. 
Agave Americana, with several relatives, was found in abun- 
dance on this part of the route ; Argemone Mexicana, white, yellow, 
or rose-coloured, was frequently met with; Samolus ebracteatus 
occurred in moist places thus far inland, and on these elevations, 
while before it was only known as a littoral plant; JJalvacee, 
Oenothera, Asclepiadacee, Gilie, Solanee, Justicie, shrubby 
Latiate, were collected of many different species; but the great 
characteristic of the country were the shrubs forming the often 
impenetrable thickets, called “chaparrdls.’’ They are mostly 
spinous, very much branched, often with remarkably small leaves, 
and not rarely with edible fruits. Amongst them many rham- 
naceous and celastraceous shrubs, and some Huphorbiacee, were 
particularly conspicuous, as well as some J/imosee, one of which 
I must not forget to mention, because it is perhaps the smallest 
shrub in this family; not more than one or two inches high, 
with diminutive leaflets, but large purple flowers; it was col- 
lected near Chihuahua. 
One of the most offensive of these chaparral-shrubs was the 
Keberlinia, Zuce., called Junco, (Gregg.); a small tree rather 
than a shrub, about ten feet high, stem four to six inches in 
diameter; wood hard, dark brown with white alburnum; ter- 
minal branches green, with a dark brown spinous point, 
one to two inches long, and one and a half to two lines in dia- 
meter; very small subulate leaves soon deciduous; small white 
flowers in short lateral racemes; fruit not seen; in flower in 
May. It was frequently seen from south of Chihuahua to Mon- 
terey, (and Matamoros. Gregg.) _ ; 
- We find here again the interesting C/ilopsis mentioned above, 
also Larrea glutinosa, and another zygophyllaceous shrub, a 
true Guajacum, which appears to be an undescribed species ; 
it belongs to those plants that connect the Mexican with the 
Texan flora, as we find it extending from Parras to Monterey, 
