Alternating Annual and Biennial Habit. 291 
their peculiar character than many of the most recently 
arisen variegated sorts. They are highly variable and 
give rise in many cases almost every year to green des- 
cendants, on the one hand, and to pure yellow, on the 
other. The former are regarded as atavists, the latter, 
however, are only variants and not mutants, since so far 
as the observations extend they give no hope that they 
will ever form the basis of a pure yellow race. These, 
the true aurca varieties, have only arisen in relatively very 
rare cases ; possibly from variegated types but without 
showing any evidence to support this supposition. 
The capacity for producing variegated leaves or yel- 
low seedlings is more widely distributed in the vegetable 
kingdom in a latent and semi-latent condition than per- 
haps any other character. 
25. ALTERNATING ANNUAL AND BIENNIAL HABIT. 
One of the strongest pieces of evidence for the doc- 
trine of mutation is the phenomenon in beets which is 
called bolting or shooting. It can be observed in almost 
every field of beets. Occasional plants are seen to de- 
velop a stem in the first year, to flower and to bear seed. 
They store no sugar or other food-stuffs or at any rate 
only to a very slight extent in their roots which become 
correspondingly woody. They are useless for practical 
purposes. On good fields about 1 % of the plants ordi- 
narily behave like this, and more rarely a smaller per- 
centage of the whole crop. Under unfavorable circum- 
stances, however, their number often increases consider- 
ably ; reaching for instance from ten to twenty per cent 
and sometimes still more. 
No farmer uses the seeds of such annual plants for 
