Senecio prcecox, D. C, frovi Mexico. 33 



New Holland, Xanthorrlioca hastilis is peculiar ; likewise in the 

 limited confines of the Pedregal Scnccio prcecox is a prominent 

 and conspicuous element of the flora, and is therefore of geo- 

 graphic importance. 



Senecio prcecox — the tree groundsel — was first described by 

 Cavanilles (1794, Icones et Descriptiones Plantarum, iii, 

 23 t. 244), as Cineraria prcBcox, and this mistake was con- 

 curred with by Willdenow (Sp. PI., v, 3 p., 2078), Sprengel 

 (Syst. Veget., v, iii, p. 546,) and De CandoUe (Hort. Genev., 

 t. 7). De Candolle in his Prodromus (vi, p. 431) transferred 

 the plant from the genus Cineraria to Senecio, thus correcting 

 the mistake into which the Spanish priest and botanist had 

 fallen. The plant is a native of Mexico, and according to 

 Hemsley (Biologia Centrali-Americana ii, 246), it has been 

 collected at the following places and by the following botan- 

 ists : North Mexico, region of San Luis Potosi, 6,000 to 8,000 

 feet (Parry and Palmer, 540) ; South Mexico, Valley of Mex- 

 ico (Bourgeau, 178) ; around Toluca (Andrieux, 295) ; Guan- 

 ajuato (Hertweg, 123); Tlalpam Pedregal (Harshbcrger) ; 

 without known localities (Mairet, Mogino, Bates, Pringle). 



Morphology. — ^The plant reaches, when fully matured, a 

 height of three or four feet and usually stands upright with- 

 without any lateral branches (Plate VII, Figs, i and 2). 

 These, however, occasionally appear at the side and by their 

 growth soon overtop the main stem, or the stem may bifurcate 

 in such a manner as to present a wide, open fork (Plate VIII, 

 Figs. I and 3). The stem is cylindrical and from an inch in ordi- 

 nary specimens to nearly two inches in diameter in the larger 

 ones. It is fawn colored in the living state, the coloring 

 being due to the smooth, corky bark which envelops it. The 

 surface is marked closely by prominent crescent-shaped leaf 

 scars, by large warty-looking lenticels, and by dormant buds, 

 which may start into activity at any time, although they appear 

 in most specimens dry and wrinkled (Plate VII, Fig. 3). The 

 outline of a typical plant is broken in many cases by the 



3 



