FACTORS INFLUENCING FLOWER SIZE IN NICOTIANA 335 
1911 by Professor Setchell and Fi flowers were measured in 1912. 
These plants, also, were cut back early in 1913 and were fully in 
flower during May of the same year. Cuttings of certain of the 
Fi H44 plants were rooted in the greenhouse during the fall and 
flowered under glass in the early spring. Another sowing of H44 was 
made in 1913 but no measurements were taken upon the flowers of 
these plants. 
The technique of taking the measurements on spread or diameter 
of corolla limb was the same as that used in the previous studies on 
the inheritance of flower size in Nicotiana (cf. Goodspeed, 1 91 2, p. 138). 
The measurements of spread of corolla limb herein listed were taken 
without the use of any holder and with the corolla limb supported 
between the thumb and forefinger. Length of corolla tube was 
taken to be the distance from the point of union of calyx and pedicel 
to the point where the under side of the reflexed limb joins the corolla 
tube. In the case of species of Nicotiana here dealt with the flowers 
were fully open throughout the day as contrasted with the more or 
less vespertine N. acuminata varieties and their hybrids, which were 
studied previously. 
III. Factors Influencing Flower Size 
I. Age of Plant'' Factor 
The heading " 'Age of Plant' Factor" has to do with the fact that 
a tobacco plant during the first few days after coming into flower 
bears flowers which differ in size from the flowers which it bears later 
in the growing season normal for this particular species or variety. 
It also serves as a heading for the discussion of the fact that the flowers 
borne on plants cut back and growing on their own roots a second sea- 
son differ in size from the flowers borne on the same plants the first year. 
The following tables (Tables I to V) are intended to illustrate the 
situation with reference to early and late flowering on the same plant. 
These are condensed statements of the full records and have to do 
with the frequency distributions for the entire population in each case. 
On account of their extent it would hardly be possible to include the 
complete records for each plant on the different dates on which the 
flowers were measured. 
In the tables the plants are arranged according to the mean flower 
size of the particular date or period in question. The mean flower size 
