Euphorbiaceae. 



often more than 10 inches. The trunk is vested in a pinkish, rather thin bark 

 which is smooth when young, but often forms thick knobs which are deeply 

 wrinkled in very old trees. It has a tremendous liow of latex, which does no* 

 coagulate on the tree, but becomes yellow, especially in old trees. 



The species occurs in the gulches back of Makawao, Maui, and also on the 

 slopes of Mauna Kea, Hawaii, near the crater Nan, 011 the boundary of the 

 Parker and Horner ranches. The writer met with it also on the Island of Lanai 

 in the dry gulches of Mahana. 



The new variety, however, occurs only on the slopes of Hualalai between Hue- 

 hue and Puuwaawaa, Hawaii, at an elevation of 3000 feet, on the rough aa lava 

 fields and also in the more humid forest of Waihou. The area with which this 

 tree is practically covered amounts to about 5000 acres. During a recent visit in 

 North Kona, engaged in botanizing in this most interesting locality, the writer 

 was struck by the tremendous flow of latex and the large amount which could 

 be procured from a single tree. Thinking it worth while to take some latex 

 samples for examination, the writer sent a large bottleful to the U. S. Agricul- 

 tural Experiment Station in Honolulu for analysis. 



This Station has since published the results of the analysis in the form of a 

 Press Bulletin No. 37, entitled "Euphorbia lorifolia, a Possible Source of Eubber 

 and Chicle," by Win. McGeorge, Assistant Chemist, and W. A. Anderson, Su- 

 perintendent Rubber Substation 



Euphorbia Rockii Forbes. 



Koko. 

 (Plate 101.) 



EUPHORBIA ROCKII Forbes Occas. Pap. Bernice P. Bishop Mus. Vol. IV. 3. (1909) 38, 



pi. 1. 



Leaves opposite, obovate-oblong, obtuse, uneven-sided with a clasping base, nearly 

 sessile, 8 to 12 cm long, 2.5 to 3 cm wide; flowers in open axillary cymes 3 to 3.5 cm long; 

 involucre campanulate, minutely hairy or glabrous on the outside, pubescent on the inside, 

 lobes ovate, minute, glands transversely oblong, not appendiculate; style branches short, 

 nearly free; capsules large 18 to 24 mm. glabrous, pink or dark crimson, on nodding 

 peduncles. 



This tree, which was discovered by the writer in August, 1908, when in full 

 fruit is exceedingly handsome. It reaches a height of about 15 to 20 feet, with 

 a trunk of about eight inches in diameter. The bark is smooth and whitish. 

 Like all Euphorbiae, it exudes a sticky, milky sap when bruised. The branches 

 are flat and spreading, giving the trees a broad, flat crown. The flowers are 

 small and inconspicuous and are borne on dichotomous cymes. The three-cor- 

 nered capsules are bright pink or deep scarlet when mature, of an inch or more 

 in length clothing the whole crown in scarlet, which is beautifully contrasted 

 with the dark-green, glossy, sessile foliage. 



The Enplwrbia Eockii is peculiar to the Island of Oahu, and is only found 

 on the windward side, in the mountains of Punaluu above Kaliuwaa valley, at 

 an elevation of 2000 feet or more. On the summit ridge it grows to a shrub, 



261 



