SIGNIFICANT ACCURACY IN RECORDING GENETIC DATA 21 7 
reasons. The true state of affairs is masked, therefore, when this 
decrease is treated as a gradual drop in flower size during the season. 
If measurements on greenhouse cultures grown in proper sized pots 
are taken daily over a long period, they simply show comparative 
uniformity in flower size until about the end of the flowering season. 
Then a decrease which produces a sharp bend in the curve occurs. 
As to variation in size owing to age of the flower, I have found that 
this is largely a mechanical difficulty. There is no difference in length 
between flowers before and after anthesis, for anthesis takes place 
normally either before or within lo hours after the flower opens in all 
species of Nicotiana under Boston conditions. A flower if unpoUi- 
nated may open for as many as 5 successive days, and there is a slight 
increase in both length and spread of the corolla. But a pollinated 
flower seldom opens on more than two successive days. The flower 
becomes less firm however and the spread of the corolla may appear 
to increase. 
Flowers of the same relative position on vigorous branches are the 
same size whether they be on the main stalk or on laterals in species 
like N. forgetiana and N. alata grandiflora which are characterized by 
vigorous lateral branches from the base of the stem. Flowers on 
lateral branches in species like N. tahacum where the main stem is so 
much more vigorous, average (in my counts) slightly less (under i mm.) 
than those on the main stem. 
After about the sixth flower on the species having racemes, and on 
the flowers coming out after the first full glory of the panicled species, 
there is also a slight decrease in size owing to decrease in the conducting 
channels of the fibro-vascular system. 
What information do these observations, which are the preliminary 
"qualitative" tests made in every investigation, give us? They show 
that to record the phenotypes of flower size of a series of Nicotiana 
plants, the seeds should be sown at the same time in uniform soil, the 
plants should be pricked out uniformly and set at the same time in a 
plot of uniform fertility. The flower records should be made within 
two or three weeks of each other at the first of the season, allowing no 
marked climatic change to intervene if possible. The flowers recorded 
should be the vigorous flowers (as stated in the last paragraph) of 
vigorous branches, and should be measured on the same day that they 
open. 
This procedure should be followed where it is physically possible, 
