14 MR. F. N. WILLIAMS ON THE GENUS SILENE. 
in the genus, and the speciousness of such a line of cleavage 
is best explained in his own words, which are here translated 
from ‘FI. Orientalis,’ vol. i:—‘‘ A genus very difficult to break 
up into groups of species, since the characters for defining 
sections are either absent or not strongly marked. Thus 
Godron demonstrated that all forms of inflorescence which 
were met with in the genus, the dichotomy, the panicle, the 
unilateral raceme, are only modifications of the cyme, and that 
they pass one into another in allied species, and even in plants 
of the same species. The number of the nerves of the calyx 
varies in plants otherwise alike in all their characters. 
Alexander Braun pointed out a character depending on the 
imbricative (quincuncial) sstivation of certain species, but 
this mode of overlapping of the petals in estivation in the 
genus is not really quincuncial (arising, as it were, from spiral 
insertion of the petals), but is a deformation of convolute 
estivation (arising from verticillary insertion), to which, in 
allied species and often in the same species, it returns. The 
seeds, which are generally canaliculate on the dorsal surface, 
may become plane, then convex, and, finally, in Helvosperma, 
carinate [with the rows of tubercles transformed into crested 
spines*]. With these considerations, I have not proposed 
sections such as it would be incumbent on a future mono- 
grapher of the whole genus to specify, but I have attempted 
to arrange the Eastern species in natural groups, as far as 
I was able, according to general characters and habit in the 
absence of definite and well-marked characters.” Boissier 
says how he tried first one character, and then another, and 
afterwards a combination of two or more, only to find that 
his hypothetical sections invariably either overlapped one 
another or failed to include some of the species. 
Rohrbach first of all divides the genus into two subgenera:— 
(1) Behen, in which the leading character is “ sestivatio peta- 
lorum imbricativa” ; and (2) Silene proper, in which the leading 
character is “ mstivatio petalorum alternatim contorta.” In 
connection with this I should like to refer to an interesting 
letter from Alexander Braun to J. Gay, preserved in Herb. Kew. 
In this letter diagrams are given of the mode of overlapping of 
the petals in estivation in Silene Pumilio; and quoting from a 
letter from Pacher, he says that usually the petals are imbricate 
in wstivation in this species, but that this is not constant, and 
* Not in the original. 
