88 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Mexican species which although they differ conspicuously among 
themselves, closely simulate a parallel series of Viguieras. As 
examples of this parallelism may be mentioned 
G. ensifolia with the habit of V. blepharolepis. 
G. megacephala, var. simulans with the habit of V. eacelsa. 
G. decumbens with the habit of V. ghiesbreghtii. 
G. ghiesbreghtii with the habit of V. buddleiaeformis. 
This simulation has various degrees of closeness. In @. ghies- 
breghtii and V. buddleiaeformis, although the similarity is striking, 
the heads are always perceptibly smaller in the Viguiera. G. me- 
gacephala var. simulans and G. decumbens, however, so closely 
resemble V. excelsa and V. ghiesbreghtii respectively, that no 
satisfactory external characters have as yet been found by which 
to separate them. The examination of the achenes, however, at 
once reveals striking differences. The achenes are in the Gymno- 
lomias more compressed, quite glabrous, and completely destitute 
of pappus. In the Viguieras on the contrary they are thickish, 
obtusely 4-angled, upwardly villous, and provided with two stout 
persistent awns and several short intermediate scales. Were the 
pappus difference the only one, these viguieroid Gymnolomias 
might logically be reduced to “ formae epapposae” of their pappus 
bearing counterparts in Viguiera, there being in Calea and else- 
where undoubted examples of the presence and absence of pappts 
in what must be regarded as conspecific types. In Gymnolomia, 
however, the difficulty is increased by the presence of other although 
slight differences in the form and pubescence of the achene. 
The writers have carefully considered the possible readjustment 
of generic lines in such a manner as to bring together the species 
of similar habit, but they have failed to find any way in which this 
could be accomplished without the union of heterogeneous ele- 
ments or an inordinate multiplication of genera founded upo” 
rather trivial characters. It has accordingly seemed best to mail- 
tain the genus Gymnolomia in its traditional interpretation, 
although there may be some artificiality in the classification ° 
the large-headed forms. Further collections will doubtless throw 
much light, if not upon the genetic affinities, at least upon the 
validity or inconstancy of the characters by which they are now 
_ separated. 
