1921] CHAMBERLAIN—GROWTH RINGS 295 
to get material for demonstration purposes, and it was surprising 
to find growth rings so conspicuous that they could be seen where 
the stem was cut with an ax. Pieces to show both primary and 
secondary structures were preserved in formalin, and later Aloe 
pleuridens, A. ciliaris, and Dracaena Hookeriana were collected 
for comparison. 
Fic. 1.—Aloe ferox at Cathcart, South Africa, January 1912; about 3m. in 
height. 
Aloe ferox in the field presents a picturesque appearance, 
looking as if an Agave had developed a tall trunk (fig. 1). It 
is associated with other xerophytic plants as bizarre as itself, 
among them tree forms of Euphorbia more than a dozen meters in 
height, species of Encephalartos, and others not so large but equally 
peculiar. Most of the material was collected near Grahamstown, 
South Africa, in January 1912, from a stem 15 cm. in diameter and 
about 3m. high. In transverse section the zone of secondary xylem 
