220 BRITISH PLANTS 
and Hooker regard all the forms of the water-buttercup as 
inconstant varieties of one species, which they name 
Ranunculus aquatilis ; in Babington’s Flora, fifteen of 
these varieties are raised to specific rank. Bentham and — 
Hooker divide the hawkweeds (Hieracium) into four 
species. This variable genus has been split up by others 
into a bewildering multitude of species. In Babington, 
the number of critical forms described as true species is 
210, besides numerous sub-species and varieties. Other 
genera with polymorphic species are the bramble (Rubus), 
Rosa, Euphrasia (eye-bright), and Saliz (willow). 
What, then, is there to guide us in this matter? In 
the first place, we must know exactly what a variation is, 
and, fortunately, upon this considerable light has been 
thrown during the last few years. 
Variations are of two kinds : 
1. Inconstant Variations, due to the environment, such 
as accidents or inequalities in light, soil, climate, or 
nutrition. These affect, within certain limits, the form, 
size, hairiness, and duration of the leaves and shoots, the 
general habit of the plant, and, in some cases, the colours 
of the flowers. These qualities, however, are not con- 
stant. They are characters acquired by the individual 
plant as adaptations to its environment. If the environ- 
ment changes, these characters change, too. They are 
not transmitted, but every plant gradually assumes them 
during its own individual life, providing the conditions 
favourable for their production are present. Such 
varieties have no right to rank as critical species ; they 
are merely forms, not distinct and constant races. Thus 
the prostrate maritime variety of broom found in Corn- 
wall (Cytisus vulgaris, var. prostratus) is a mere form, 
with no claim to specific or even varietal rank, any more 
than luxuriant garden specimens have. The seeds of this 
plant, when sown in the garden, grow into the ordinary 
form of broom. 
2. Constant Variations.—These are not dependent upon 
accidents of environment, and always breed true to seed. 
They are true races, and have a right to rank as species, 
if the species is to be regarded as the unit of classi- 
fication. 
In practice, however, the difficulty is to decide what 
variations are constant and what inconstant, and the 
