402 BOTANICAL GAZETTE [JUNE 
have as many ducts as the more recent, an indication according to 
the present view that this plant might formerly have been irrigated. 
The owner of the field in which the non-irrigated specimen is found 
tells me that such, indeed, is the case. 
Fic. 2.—Celtis pallida: left, not irrigated; right, irrigated. 
ha 
mountain on which the Desert Laboratory is situated. The irrigated 
CELTIS PALLIDA (fig. 2).—The non-irrigated plant grows on the 
Fic. 3.—Covillea tridentata: left. not irrigated; right, irrigated. 
plant is on the grounds of the University of Arizona, and has been 
watered occasionally. 
CoVILLEA TRIDENTATA (jig. 3).—The non-irrigated plant is on 
the mesa at the northern base of the laboratory mountain. The 
