12 J.D, Hooker, Introductory Essay to the Flora of Tasmania, 
little tendency to reversion.* With this law the suggestive ob- ] 
servation of M. Vilmorin well accords, that when once the con- 
stitution of a plant is so broken that variation is induced, it 1s ’ 
easy to multiply the varieties in succeeding generations. 
It may be objected to this line of argument that our cultivated 
lants are, as regards their constitution, in an artificial condition, 
ture’s laws in producing a new variety of wheat,—we ma have 
only anticipated them; nor is its constitution impaired because 1t 
peculiar condition of the plant itself, and still less to any change 
effected by man upon it, that its annual extinction is due, but to 
causes that have no effect whatever upon its own constitution, 
and over which its constitutional peculiarities can exercise nO 
control. 
_11. Again, the phenomena of cross impregnation amongst in- 
dividuals of all species appear, according to Mr. Darwin’s accu- 
rate observations, to have been hitherto much underrated, both 
as to extent and importance. The prominent fact that the sta- 
mens and pistil are so often placed in the same flower, and come 
to maturity at the same epoch, has led to the doctrine that flow- _ 
ers are usually self-impregnated, and that the effect is a conserv- 
ative one as regards the permanence of specific forms. The ob- 
* It is not meant by this that any character of a species which may be lost in its 
ha : 
variety never reappears in the descendants of the latter, for some occasionally do 
so in great force ; what is meant is, that the newly acquired characters of the va- 
a ee obliterated that it has no longer a claim to be considered 
