1913) YORK—DENDROPHTHORA 95 
arranged as in the latter, but they often show a tendency toward 
a decussate or whorled arrangement. The plants are distinctly 
dioecious, both forms being exactly alike in external appearance, 
except that the staminate flowers are usually more densely crowded 
on the spikes. The anthers are unilocular and sessile on the seg- 
-ments of the perianth. D. gracile was found at altitudes of 5000- 
6500 ft., in well exposed places. It was observed mostly on 
Vaccinium meridionale. 
The spikes 
Since these two species of Dendrophthora are so much alike, the 
following descriptions, which are drawn primarily from D. opun- 
tiotdes, will be understood to apply to both unless otherwise stated. 
Each spike is usually composed of two or three internodes, and at 
the base of each internode there is a pair of connate bracts (figs. 3, 
6). Primary growth of this axis is accomplished by the activity - 
of an apical group of initials (fig. 2). ‘There is considerable second- 
ary elongation of the spike, due to an intercalary growth zone at 
the base of each internode. 
A single pair of flowers is usually borne in each internode with 
the exception of the basal one (fig. 3). They arise laterally just 
below the apex of the spike, and are at no time closely associated 
with: the bracts at the base of the internode, that is, they do not 
seem to be axillary in position (figs. 4, 5). In other spikes, which 
occur less frequently, there are often two or three pairs of flowers 
on each internode; of these the terminal pair is evidently older, 
and if three pairs are present, the basal pair is youngest of all 
(fig. 6). The appearance of these internodes, when the flowers 
are nearly mature, suggests that the second and third pairs have 
arisen successively during the intercalary growth of the internode, 
and that they have arisen from the young tissue at the base of the 
internode while this portion was still surrounded by the subtend- 
ing bracts. This phenomenon, which seems unusual in these species, 
was noted by EIcHLER (7) in Dendrophthora Mancinellae Eichl., 
and is a characteristic feature, for example, of the inflorescence of 
Phoradendron crassifolium Pohl., where the number of flowers on 
each internode is much greater than in D. opuntioides. 
