t;
but if only four or a lesser number of species originally existed, then
it is evident that varieties so strongly marked have arisen, that they
have been considered by capable judges as specifically distinct. But
the impossibility of deciding which forms ought to be ranked as species
and which as varieties, makes it useless to specify in detail the
differences between the various kinds of wheat. Speaking generally, the
organs of vegetation differ little;[543] but some kinds grow close and
upright, whilst others spread and trail along the ground. The straw
differs in being more or less hollow, and in quality. The ears[544]
{314} differ in colour and in shape, being quadrangular, compressed, or
nearly cylindrical; and the florets differ in their approximation to
each other, in their pubescence, and in being more or less elongated.
The presence or absence of barbs is a conspicuous difference, and in
certain Gramineae serves even as a generic character;[545] although, as
remarked by Godron,[546] the presence of barbs is variable in certain
wild grasses, and especially in those, such as _Bromus secalinus_ and
_Lolium temulentum_, which habitually grow mingled with our cereal
crops, and which have thus unintentionally been exposed to culture. The
grains differ in size, weight, and colour; in being more or less downy
at one end, in being smooth or wrinkled, in being either nearly
globular, oval, or elongated; and finally in internal texture, being
tender or hard, or even almost horny, and in the proportion of gluten
which they contain.

Nearly all the races or species of wheat vary, as Godron[547] has
remarked, in an exactly parallel manner,--in the seed being downy or
glabrous, and in colour,--and in the florets being barbed or not
barbed, &c. Those who believe that all the kinds are descended from a
single wild species may account for this parallel variation by the
inheritance of a similar constitution, and a consequent tendency to
vary in the same manner; and those who believe in the general theory of
descent with modification may extend this view to the several species
of wheat, if such ever existed in a state of nature.

Although few of the varieties of wheat present any conspicuous
difference, their number is great. Dalbret cultivated during thirty
years from 150 to 160 kinds, and