Altcrnatincj Annual and Biennial Habit. 291 



their peculiar character than many of the most recently 

 arisen variegated sorts. They are highly varialjle 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 BIENNL\L 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 

 onlv to a verv slipiit 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 pcv- 

 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 



