Water Storage and Conduction in 5enecio 

 praecox, D.C., from flexico. 



(WITH PI.ATE8 ril ANJ> Till.) 



By John W. Harshberger, Ph. D, 



[Read before the " Society for Plant Morphology and Physiology" at Ithaca, Decem- 

 ber 29, 1897. Abstract published in " Science " January 28. 1898.*] 



WITHIN 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. 



t 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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