FACTORS INFLUENCING FLOWER SIZE IN NICOTIANA 369 
an early provision for seed production. As the plant grows older, 
however, the products of metabolic activity begin to be shared by 
both vegetative and floral organs until finally it is possible to find the 
vegetative characters suffering in favor of the reproductive characters. 
Reactions normally proceeding in one direction are forcibly reversed 
or perhaps reaction products are not allowed to accumulate in the 
usual regions and the metabolic reactions reach a point of equilibrium 
at a later period and in another portion of the plant. Similarly what 
is recognized as a periodicity in the production of flowers means the 
concentration of the products of metabolic activity in different regions 
at different times to accomplish special and individual results. That 
some such process must be operative is seen in the common practice 
on the one hand of increasing vegetative growth by the elimination 
of the floral organs and of restricting maximum vegetative growth to 
favor the early development of characters connected with the repro- 
ductive organs (cf. Cook, 1914) on the other hand. We feel that the 
observations tabulated on the preceding pages demonstrate the fact 
that under such normal, inherent conditions attending development, 
the size of flowers will vary to a significant extent. The first flowers 
produced by the vigorously growing plant are larger than those 
produced near the end of the flowering season when vegetative growth 
is at an end. An elimination of all the seed that starts to mature is 
effective in shifting the whole normal period of development. When 
the formation of seed is prevented, the normal life of the plant may 
be doubled and the size of the flowers it bears will remain remarkably 
constant throughout the entire duration of life. 
In the light of these facts, the behavior of flower size in the case of 
the almost completely sterile Fi hybrids dealt with in the preceding 
pages, is interesting and significant. These species hybrids are in 
general replicas on a larger scale of their N. Tahacum parent, but they 
inherit a short lived perennial habit from their N. sylvestris parent. 
Under field conditions as they exist here these Fi hybrids reach their 
maximum vegetative and floral development relatively early in the 
growing season normal for their parents, and maintain it with only 
slightly diminished vigor for four or five months. There follows a 
rest period of from one to three months during which the plants are 
only feebly flowering and portions of the vegetative organs die back. 
With the rainy season there comes the production of new laterals and 
new flowers which are larger than the flowers produced toward the 
