36 Harshberger — Water Storage and Conduction in 



A question which very naturally arises in studying this plant 

 is : How is the water prevented from being lost at the surface ? 

 The answer is found in the structure of the cortex. The bark 

 consists of tabular cells arranged in a number of layers out- 

 side of the cortex proper, which is green to a considerable 

 depth. Prominent in the cortex are reservoirs filled with a 

 balsam-like fluid which hardens upon exposure to the air. 

 These balsam receptacles are found in two positions in the cor- 

 tex, under, near the phelloderm, in the exocortex, and next 

 the bast in the endocortex. When a section is cut, the liquid 

 exudes, hardens and thus closes the wound. Aeration of the 

 stem is accomplished by the lenticels. 



Upon a priori grounds, the pith stores up water in Senecio 

 prcBcox during the rainy season for the use of the plant during 

 the dry period, when the flowers shoot forth and the seed is 

 produced at the expense of the reserve water. Have we evi- 

 dence that such is the procedure ? 



Fortunately, a fully developed stem (Plate VII, Fig. 3) was 

 collected on August 27, 1896, on the Pedregal near Tlalpam. 

 It was carried to Philadelphia in a trunk and laid aside in the 

 dry state for a number of months. Upon examination, it was 

 found to have sprouted. Short lateral branches with unde- 

 veloped leaves soon appeared, and for the last sixteen months 

 without water or soil, the growth has gone on, until at this 

 writing, December 24, 1 897, the dry stem shows at least four 

 green branches (Plate VII, Fig. 3 ; Plate VIII, Fig. 2 a), tur- 

 gescent and tipped by a number of small green leaves. These 

 four branches measure respectively lyi, i}{, 1, ^ inches. 



Sections of this dry stem show the cortex region to be 

 practically as turgescent as when first collected, the balsam 

 exuding when a section is cut. The wood, too, appears normal 

 in color and somewhat moist to the touch. The pith, how- 

 ever, is dry ; the water has been removed from the discs, which 

 are dry, paper-like and extremely brittle (Plate VIII, Figs. 2 a 

 and 2 b). The spaces between the successive discs, or lamellar 



