EOBIXSON, — STUDIES IN THE EUPATORIEAE. 29 



ular puberulence. Like Brachyandra, Addisonia has an invclucre 

 with o-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, has 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 obvio'js relationship and to avoid the adoption of a standard of 

 generic classification solely on the basis of involucral diff'erences, 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 Trichogonia, 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 fi-om 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 style-branches more expanded than is 

 really the case. To this may be added the circumstance that Bentham 

 long ago referred the genus to the Piquerinae, with which it has no 

 close affinity. The original description of Leto states that the corolla 



