VOLUME LXXIII NUMBER 6 
THE 
BOTANICAL GAZETTE 
“fune 1922 
VARIATION S IN CYTOLOGY AND GROSS MORPHOLOGY 
OF TARAXACUM 
II. SENESCENCE, REJUVENESCENCE, AND LEAF VARIATION 
N TARAXACUM 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 295 
Paut BIGELOW SEARS 
(WITH NINE FIGURES) 
The variability of Taraxacum has frequently been recorded 
in botanical literature without receiving much elucidation. It is 
less often an object of investigation than of conjecture and dis- 
cussion. A few botanists have studied the effect of environmental 
factors upon Taraxacum, but their results have not cleared away 
taxonomic difficulties. Systematic botanists have either looked 
upon the variations in this genus as fluctuations or slight mutations, 
and then proceeded to lump or split as judgment might dictate. 
That life history exerts a profound influence upon form seems gener- 
ally to have escaped attention. 
The 1910 supplement of Index Kewensis (12) lists 152 new species 
as described within five years, mainly from Scandinavia. Leaving 
aside such overwhelming evidence of polymorphy, it is interesting 
to note that the painstaking monograph of HANDEL-~MAzETTI (10) 
admits fifty-seven species. These fall into eleven sections. Of 
these eleven sections four are so distinctive that none of their species 
have been mistaken by preceding students for either T’. vulgare or 
T. laevigatum. In each of the remaining sections species have 
425 
