258 BOTANICAL GAZETTE. [ October, 
cross-section of a stem four years old, in which only two of 
the wings show the furrow, owing to the fact that at the 
point where this section was cut, the furrows of the remain- 
ing three wings were not perfectly developed. As the phel- 
loderm plays no important part in the formation of cork from 
the standpoint of our subject, no attention was given to this : 
throughout the study made. : 
Philadelphia, Penn. , 
eT 
Characteristic vegetation of the North American desert. 
DR. GEORGE VASEY. 
The term desert has a somewhat wide application. In 
one sense it is applied to a tract of country practically desti- 
tute of vegetation from sterility of soil. Such sterility, how- 
ever, is not always the fault of the soil, but is due to the 
absence of water in sufficient quantity to promote vegetation. 
Our ideas of a desert are largely drawn from popular de- 
scriptions of some portions of the Great Sahara, where low 
plains covered with drifting sand, interspersed with vast 
fields of naked rock, spread over regions over which the 
vegetation of palms, ferns and acacias. But this description 
covers only a part of what is known as the Sahara Desert. 
—~ 
each other by valleys, immense sandy tracts at a general § a 
vation of from 1,200 to 1,500 feet, but sinking at times gn 
depressions which sometimes descend below the level of t 
sea, ; 
_ The moisture from the Mediterranean Sea is arrestee 
Its southward Passage by the range of mountains running 
nearly parallel with it, and is mainly prec:pitated on the 
north or Mediterranean side; thus the southern slopes at 
left in an arid condition, the aridity increasing as the county 
. m i 
falls in the Winter, and, melting in the summer, runs uox 
the narrow courses and ravines until it is finally wasted 7 
