334 
GENETICS: GOODSPEED AND CLAUSEN 
The conclusions drawn in this paper are based on some 25,000 measure- 
ments taken on the following pure lines and hybrids of Nicotiana: 
1. N. Tahacum var. macrophylla^ in the growing season 1913. This 
N. Tahacum variety has been grown at the University of California 
Botanical Gardens for six years in the pure line, under the garden number 
22/07. 
2. The Fi hybrid, N. Tahacum var. macrophylla X N. sylvestris,^ 
which will be referred to as FiHss. Flowers of this hybrid were meas- 
ured on plants from the first sowing of the hybrid seed in 1912, on the 
same plants cut back and coming up from the roots in 1913, and on a 
second sowing of the same hybrid seed in 1913. 
3. FiHi37, the reciprocal of the above cross, flowers of which were 
measured in 1913. 
4. The Fi hybrid produced by crossing the Fi of the hybrid N. Tahacum 
var. Maryland X N. Tahacum var. Cavala with N. sylvestris, the garden 
number of which is H44. As with H38, flowers of this hybrid were first 
measured in 1912, and again on the same plants cut back and coming 
up from the roots in 1913. In addition cuttings of these plants were 
made and measurements taken on them. 
From the data on these and other populations it has been found possi- 
ble to determine a number of factors which influence flower size in 
Nicotiana. For convenience these are treated under various rather 
arbitrarily selected headings. Under the 'age of plant' heading are 
included not only a consideration of the difference in the size of flowers 
borne early in the season as compared with those borne late in the season 
on the same plants, but also a consideration of the difference in the size 
of flowers the first blooming season of the plant compared with the size 
of the flowers produced the second year on the same plants cut back and 
coming up from the roots. Under the 'age of flower' heading are included 
first, a consideration of the difference in the size of flowers borne on the 
terminal inflorescences just going out of flower and those borne at the 
same time on laterals and second, the influence of age on the individual 
flower; i.e., comparisons of measurements of flower fully opened, before 
and after shedding pollen. Other factors such as the influence of the 
removal of flowers and developing seed capsules, the behavior of cuttings 
under various conditions, and the influence of soil fertility have likewise 
furnished data upon this variabiUty of flower size under conditions 
attending development. 
When plants first come into flower the spread and length of corolla 
are greater than the spread and length of flowers produced on the same 
plants later in the growing season. Thus the mean spread of corolla 
