4 MR. F. N. WILLIAMS ON THE GENUS SILENE. 
they are closely allied to one another and ought certainly to be 
included in the same genus, they are readily distinguishable as 
species; and it would be an unnatural separation to transfer 
the former to another group altogether, or to set it up as the 
type of a new genus. Then, again, we have Braun’s observa- 
tions from living specimens, in which faint commissural nerves 
are sometimes to be found, and at other times the nerve loses 
its commissural character by bifurcating at the base of the 
calyx into two branches, so that each segment of the calyx 
appears to have three nerves. Here, then, is a fresh proof, if 
one were needed, for the maintenance of the position that 
within the limits of the same group of plants, the classifi- 
catory value of a character, often of more than generic 
importance in single genera, at the most made use of for 
the discrimination of species, can be even altogether worthless, 
without thereby undervaluing its importance as a character 
for separating groups of species. Moreover, a similar anomalous 
exception occurs sometimes in Drypis spinosa. 
I here propose the names of ‘“ Silenoidesw” and “ Gypso- 
philoidee” for the two subtribes of Lychnidew. The sub- 
order ‘‘ Silenoideswe” of Engler and Prantl* is co-extensive and 
synonymous with the suborder “ Silenines ” in the classification 
and conspectus of genera as given at the end of this introduc- 
tion. In this terminology of groups I have followed a general 
suggestion made by Mr. E. M. Holmes at the International 
Botanical Congress of Genoa in 1892. 
I will now discuss the distinguishing characters of the group 
of genera included in the subtribe Silenoidew. What are they ? 
As in other groups or divisions, the usual answer to the 
question is that all species which agree in essential characters 
should belong to one genus. But what these essential 
characters or distinguishing marks in any particular group 
may be, will depend most frequently on the critical judgment 
of the individual botanist. Niigeli lays it down that for any 
particular plant that character is to be considered as primary 
and essential which is shown to be constant. In known 
relationships, Niageli is right: a constant character is at the 
same time an essential one; but the question is, whether it is 
in general essential to the conception of the organism as a 
plant, or rather as characteristic of the order, the tribe, the 
* Die Natiirlichen Pflanzenfamilien, Theil iii (1889), 1 b, p. 69. 
