VARIATIONS IN CYTOLOGY AND GROSS MORPHOLOGY 
OF TARAXACUM 
I. CYTOLOGY OF TARAXACUM LAEVIGATUM 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 293 
PAUL BIGELOW SEARS 
(WITH PLATES IX, X) 
Introduction 
These investigations are the outgrowth of a study, begun in 1914 
at the instance of the late Professor C. E. Brssry, of partheno- 
genesis in Taraxacum vulgare (Lam.) Schrk. and T. laevigatum 
(Willd.) DC. These two species are the common ones in central 
United States, being respectively designated as Leontodon Taraxa- 
cum L. and L. erythrospermum (Andrz.) by Brirron and BROowN 
(3). In 1917 the existence of ameiotic parthenogenesis in both ~ 
species was confirmed (23) and certain pollen abnormalities briefly 
described. These abnormalities have invited more critical analysis 
as a means of throwing light upon certain phases of variation and 
degeneracy, and likewise upon the problem of synapsis. The 
study of non-cytological variations has been directed largely to leaf 
characters. This is due to frequent references in the literature of 
Taraxacum to “polymorphy” and to the wholesale erection of 
species (cf. Index Kewensis 10). 
Maturation phenomena in embryo sac and pollen have been 
homologized and found to be highly fluctuating. The fluctuations, 
instead of being anomalous, seem plainly to indicate variations in 
the duration and relative intensity of (1) chromosome individuality, 
(2) sex, (3) polarity. 
Synapsis in the sense of chromosome pairing is expressed with 
varying degrees of vigor and quite without reference to doubleness 
of the spireme thread. 
Leaf variation within the species is shown by quantitative 
studies to be a matter of senescence and rejuvenescence. The rdle 
of environment is secondary. The interplay of senescence and 
Botanical Gazette, vol. 73] [308 
