ROBINSON. — STUDIES IN THE EUPATORIEAE. 29 
ular puberulence. Like Brachyandra, Addisonia has an inveiucre 
with 3-4-seriate scales which are strongly imbricated and very unequal 
in length, but unlike any of the three other monotypes here discussed, 
Addisonia has its involucral scales arranged in four upright rows. 
This difference, if any, must be regarded as its claim to rank as a 
separate genus. It is a conspicuous characteristic, and at first sight 
might seem to be of considerable diagnostic importance. However, a 
second species, closely related to Addisonia virgata Rusby, been 
collected in Peru by Weberbauer, and in it the scales are in five not 
always equidistant erect series, showing that the number of the series 
is not of generic significance. Furthermore, the tendency of closely im- 
bricated, somewhat carinate involucral scales to assume more or less 
regularity in upright series is observable elsewhere in the Compositae 
in a way to cast much doubt upon the importance of the character as 
a sole basis for a generic separation. Thus, in the species of Bigelovia, 
of the B. graveolens group, an equally marked tendency of this sort is 
observable, but shows such inconstancy even in very nearly related 
forms, that it can scarcely be taken as a character of specific, not to 
mention generic, significance. In view, then, of the close correspond- 
ence of the four South American plants here discussed — a -likeness 
which embraces, as we have seen, not merely habit, leaf-arrangement, 
etc., but all the more significant characters of flower and fruit —it 
seems best to unite them under the oldest name, both in order to show 
their obviovs relationship and to avoid the adoption of a standard of 
generic classification solely on the basis of involucral differences, which 
would cause great difficulty and artificiality if applied to neighbor- 
ing genera of the Compositae. 
Attention may be called to the fact that all four of these plants 
maintain the chief distinction by which the genus Brachyandra has 
long been separated from the allied genus T'’richogonia, namely, the 
very narrowly tubular corolla. The creation in botanical literature 
of these four successive genera for plants, which now appear to be of one 
generic type, is readily explained and to a great extent excused by the 
rarity of the plants concerned and by the natural misapprehensions 
which have arisen from mistakes in the original descriptions. Thus, 
the original Helogyne, founded on a small tip of a flowering branch, was 
thought by Nuttall to be probably an annual, and his description was 
likely to mislead the reader into supposing that the outer involucre 
was more foliaceous and the pl he clies more expanded than is 
long ago referred the genus to the Piquerinae, with which it has no 
domstesee The original description of Leto states that the corolla 
