Water Storage and Conduction in Senecio 
przcox, D.C., from [lexico. 
(W1TH PLATES VII AND FIit.) 
By Joun W. HarsHBERGER, Pu. D. 
{Read before the ‘‘ Society for Plant Morphology and Physiology” at Ithaca, Decem- 
ber 29, 1897. Abstract published in ‘“ Science”? January 28, 1898.*] 
ITHIN a few miles of the City of Mexico on the 
/ \/ northern slopes of the Sierra del Ajusco is an extinct 
lava stream, hardened into solid rock. This coulee 
of lava, known locally as the Pedregal, extends from the 
summit of a hill called Chitle, one of the peaks of the southern 
mountain chain, down into the Valley of Mexico to the edge 
of a suburban town, Tlalpam. Of volcanic origin, it covers 
many hundreds of acres, and is extremely rough and uneven. 
It is difficult to collect plants in such a broken and uneven 
country, resembling a sea, congealed at the moment of its 
greatest turbulence. The lava is full of cracks, blisters, cav- 
erns and sinks, produced during the process of cooling. It is 
raised into cones, presents most curious sinuosities, and is here 
and there broken down into rugged, jagged protuberances, as 
sharp and cutting as a knife’s edge. 
The Pedregal is a wild flower preserve, and the vegetation is 
peculiar.t In many of the rougher portions the trees are 
practically absent and their place is taken by several plants, 
* Since the above dates an article entitled ‘La Flore des Regions Arides du 
Plateau du Mexico’? has appeared in the ‘‘ Revue General de Botanique,”’ (Feb- 
ruary 15, 1898,) by S. G. Seurat. The author confirms the statements made 
as to the growth of this plant on the lava beds of Mexico.—J. W. H. 
+ HarsHBERGER.— Science,” N. S., vi, p. 569, October 15, 1897, and vi, p. 
908, December 17, 1897. ‘Bulletin, Torrey Botanical Club,’’ xxiv, p. 178, 
April, 1897. 
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