570 
to ecological inquiries. It is an elevated 
circular valley, closed in by two distinct 
ranges of hills, the oldest porphyritic rocks 
to the north and east, which before vol- 
eanic disturbances began sloped gradu- 
ally southward toward the Isthmus, and 
the newer volcanic mountains to the south 
and west built up in a later period and 
closing off to the south and east the gradu- 
ally sloping plain, thus forming the basin- 
shaped plateau known as the Valley of 
Mexico. Ajusco, the oldest voleanic peak, 
stands like a sentinel on the southern rim of 
the basin, and from its summit to the base 
.of the valley extends a lava bed known 
locally as the Pedregal. On the southeast 
rim of the valley rises the ice-capped 
peak of Popocatapetl (17,780 feet), and to 
the eastward, connected with the conical 
voleano, the ridged backbone of Ixtacci- 
huatl, also snow-capped, considered by ge- 
ologists to be built of the older porphyritic 
rocks. Along the base of the eastern 
range three fresh-water lakes, Texeceo, 
Chaleo and Xochimilcho, are found, while 
the partially drained basin of lake Texcoco 
forms an alkaline plain stretching along 
the Mexican railroad to the hills which 
jut southward into the plain at Guadalupe. 
The lakes and communicating ditches 
furnish the hydrophytes, the alpine sum- 
mits of Popocatapetl, Iztaccihuatl and 
Ajusco (13,612 feet) the alpine plants; the 
lava beds afford a large number of xero- 
phytes, while the alkali plain near lake 
Texcoco grows a number of halophytes 
which reach their greatest numerical de- 
velopment on the Gulf coast. The rich 
agricultural soil of the valley grows a 
varied and luxuriant series of mesophytes. 
It presents in its constricted area a veri- 
table botanical garden, right at the doors of 
the population of the capital. 
Space will not permit a detailed account 
of the plants found growing in the different 
vegetable zones. Only one or two plants 
SCIENCE. 
LN. S. Vou. VI. No. 146. 
can be taken by way of illustration. The 
xerophytes show very thick leaves, thick 
cuticle and a hairy or spiny covering, and 
are usually consolidated in structure. The 
plants are peculiarly constructed so as to 
store water by means of certain mucilagi- 
nous substances which absorb moisture and 
hold it tenaciously, giving it off very slowly 
tothe air. The Agave, Maguey or Century- 
plant, commonly found cultivated on the 
plateau of Anahuac, is a typical xerophyte. 
It is to be seen growing wild in desert 
places and on lava beds, and grows in one 
or two forms to a large size (eight feet), 
weighing sometimes 600 to 800 pounds. It 
is a plant of considerable pharmaceutical 
interest. It stores up in its tissues a sur- 
prising amount of a sugary water, which 
exudes when the plant is tapped, as the so- 
called honey water or aguamiel. This 
aguamiel when fermented yields the bever- 
age called pulqué, which is consumed in 
large quantities by the poorer Mexicans, 
who pay una cuartilla (38 cents Mexican, 
14 cents American) for a glass of this 
yeasty-tasting alcoholic drink. It is ob- 
tained from the plant in the following way: 
When the Agave, which yields the liquid 
honey water, reaches adult size, turns 
slightly yellow and begins to shoot up a 
flower stock, or before that time, it is 
tapped by hollowing out a concavity in the 
core of the plant at the base of the central 
leaves, which stand upright and are not 
yet fully expanded. The pulqué-gatherer, 
with along hollow gourd pierced at both 
ends, draws the aguamiel by suction from 
the coneave place as it wells up from be- 
neath. He is clad in cheap cotton clothes 
and wears a hide apron fastened around 
his waist and a thick leather knee pad on 
his left leg. Then pressing the spiny leaves 
aside with his left knee, he pushes one end 
of his gourd with his right hand into the 
tapped place and draws upon the other end 
with his mouth, until he has filled the 
