278 
Within the family the question of generic relationship has been 
the subject of discussion. Their close resemblance in morpho- 
logical characteristics evidently entitles the five species to be 
classed in the same natural order, but under how many or what 
genera is not so clear. 
There are three genera now recognized in the order, namely, 
Empetrum, Ceratiola and Corema. In the genus Empetrum are 
two species, zigrum aud rubrum, the former being circumboreal 
and widely distributed in high altitudes, while the latter is found 
in Southern South America. There is one species of Ceratiola, 
C. ericoides, which is found in the southern United States. 
The genus Corema was named by Don after a careful study of | 
the then so-called third species of Eimpetrum, E. album. This 
plant, which was discovered in Portugal, and as yet has beea 
found only there and in the Azores, was from its general appeal 
ance and habit at first referred to Ampetrum. Later Don found 
morphological differences in the new species, notably in the num- 
ber of cells of the ovary, the kind of inflorescence and the lack of 
any proper perianth, which he considered sufficient to constitute 4 
new genus. This he called Corema, giving us the third genus of 
the Order Empetracez with the one species C. alba. 
Until 1837 these four species, under three genera, were the 
only representatives of this order known, the genus Corema not 
being known to occur in this country. 
About that date Dr. Conrad found near Pemberton Mills, New 
Jersey, a small evergreen plant which he failed to identify. Spee 
imens coming into the posession of Dr. Torrey he referred 1¢ to : 
the order Empetracez, placing it in the genus Ammpetrum, Ss e 
at the same time its agreement in some particulars with C. : 
Dr. Torrey named the new species, in honor of Dr. Conrad, 
Conradu (Ann. Lyc. N. Y., 4: 83. 1837). 
A little later Tuckerman sent very complete specimens of sate - 
new species to Dr. Klotsch in Berlin, who decided that it did peg : 
properly belong to any of the three genera of Empetrace®, © 
constituted a new genus of the same order. Accordingly, he pub- 
lished a detailed description of the new genus, calling it Th eb : 
mania, in honor of Dr. Tuckerman (7; Conradii Klotsch, wiee™ 
Arch. 7: 248. 1842). But as this generic name had already bee? 
i. 
