Floral Evolution. 
393 
function of cross-pollination. It is therefore a biological character; 
and its occurrence in both Composite and Dipsacaceae does not, we 
have seen, warrant the presumption that these are descended from 
a recent common stock. A group of plants may share a number of 
biological characters in common without being therefore nearly related. 
Other examples of this important principle which will be 
familiar to the reader are afforded by the characters of sympetaly, 
zygomorphy, epigyny, etc. We have recognized the appearance of 
sympetaly in seven distinct and extensive circles of affinity; and 
attention has been called early in the present chapter to the 
occurrence of this character as the expression of extreme floral 
advance in many and diverse groups throughout the Archichlamydese. 
Its biological advantage is so great, so to speak, that cohesion of the 
petals is seldom neglected among the many evolutionary efforts to 
secure improvement in the floral mechanism. Similarly with zygo¬ 
morphy, epigyny, and other biological characters. 
Again, it is clear that the vegetative characters of all the 
individuals in a peculiar and definite environment must within 
certain limits be in harmony therewith; hence it follows that all 
the individuals in that and similar environments may have certain 
vegetative characters in common, whatever their several ancestries 
may be. Such characters will yield no clue therefore to the 
ancestry. Whence, Characters which are produced directly by the 
environment have no value in classification. 
If on the other hand two or more plants have a common 
character which has no relation to the environment nor to any 
biological function, we can only suppose this to be due to inheritance 
from a common ancestor. We know little of the cause of variation ; 
but among the host of variations that arise in any given stock, some 
may be of little or no biological utility or significance. In so far as 
such variations are not positively detrimental to plant-life they will 
encounter no interference from the operation of Natural Selection, 
and so will conceivably be handed down by inheritance from one 
generation to another . 1 It will be convenient in the sequel to refer 
to variations and characters of this kind as fortuitous. The 
appearance of identical fortuitous characters in a number of plant- 
forms will thus create a reasonable presumption that they have 
1 This view involves more or less the idea of descent by sudden 
mutations, and many may deny that useless characters have 
persisted through long lines of descent. In this case we shall 
be thrown entirely upon biological characters for phyletic 
purposes; this aspect of the matter is dealt with in the 
immediate sequel. In any case it will be remembered that 
biological characters have been our guide throughout our 
examination of the sympetalous groups. 
