300 
approximate distribution of these two species is shown in the 
accompanying ma 
I. eR Ca, of Rhododendron micranthum Turez; 2, of Ledum 
glandulosum Nu 
It will be observed that these two areas of distribution are nearly 
in the same latitude, that of the Ledum extending slightly further 
north. The genus Ledum is undoubtedly more primitive than 
Rhododendron, on account of its polypetalous corolla, and it 
enjoys a very wide distribution in the Northern Hemisphere. 
I suggest that the origin of such a species of Rhododendron as 
R. micranthum may have been from an ancestral type similar to 
the present day Ledum glandulosum, which species has many 
characters in common, but is separated generically mainly by 
its free petals. I do not suggest that R. micranthum has arisen 
directly from the genus Ledum as it exists at the present day, 
for we have to remember that evolution has probably been 
equally rapid i in the two genera. I give below the records of the 
two species in the Kew Herbarium :— 
Rhododendron micranthum J'urcz. 
CHINA. Western Szechuan: Tchen-keou-tin, Farges 1258; 
West and near Wen-ch’uan Hsien, 6000-7800 ft., Wilson 1200; 
Lifan Ting, Wilson 1320. Hupeh: Monte Triora, "Silvestri. 1702; 
1703; Fang, Henry 6632; Nanto, Wilson 1526; Wilson 660; 
Shinde: : In-kia-po, Giralds:; Mt. Pht kas: -san, Géraldi. Shansi : 
near Hsi-po-po, Meyer 1697. Kansu: near Kwa-tsa, Meyer 1825; 
Potanin. Chili: Pekin, Bretschneider ; Top of Mt. Conolly, 
Bullock 86; rocky exposed mountain ridges, 7000-10,000 ft., 
near Hsien Wu- tai-shan, Meyer 1334; Weichang, Purdom 55. 
Ledum glandulosum N wit. 
CanaDA. Alberta: Devils Head Lake, 6000 ft., Macoun ; 
slopes of Vermillion Mt., 6300 ft., McCalla 2163. 
