1922] STOUT—STERILITY Ii7 
aborted flowers, but usually only a few of the first flowers abort. 
Flower abortion also appears in many plants of B. chinensis which 
have very loose rosettes of leaves. 
In these species flower abortion occurs as a transitional stage 
between a period of vigorous vegetative vigor and a period of flower 
formation and seed production. The plants which exhibit abortion 
are not able to pass at once into complete reproductive activity 
in producing potent flowers. The amount of abortion is greatest 
in the varieties of B. pekinensis in which vegetative vigor is most 
marked and in which excessive vegetative growth can readily be 
induced by good cultural conditions and which have been selected 
and bred for this feature. Flower abortion occurs in numerous 
plants of these sorts that are grown in pots, as it does in many 
plants of the loose-leaved kinds, but it apparently tends to be less 
marked in these. 
Flower abortion is here undoubtedly correlated with the degree 
of vegetative vigor. It is not merely due to a stifling of flowers 
from simple direct injury because of inclosure within-a head, 
however, but to a constitutional feature of which the formation 
of a leafy head or rosette is an extreme expression. In this sense 
the abortion of flowers is self-induced and to some degree hereditary. 
Usually the transition from aborted flowers to apparently normal 
flowers is sudden and complete (fig. 1). Sometimes, however, the 
first flowers to appear after the aborted ones, or the first flowers 
when there are no aborted ones, are poorly developed, are plainly 
immature and undersized, and especially in B. chinensis there may 
be premature opening. 
(2) ARRESTED DEVELOPMENT OF LAST FLOWERS.—At least some 
of the last flowers which begin to form remain immature and func- 
tionless. In the first of such flowers the corollas wither quickly 
and may become dry and papery without falling. Then the flowers 
become smaller in size and more incomplete in development until 
at last they are mere stubs of tissue. Usually from six to ten 
flowers in these various stages of arrested development may be 
counted at the tip of each branch. On short, lower, lateral branches 
and on secondary or later laterals all of the flowers may fail to de- 
velop fully. This condition is shown in the illustrations. The dis- 
tribution of flowers that fail to develop is indicated in figs. 2 and 3. 
