FACTORS INFLUENCING FLOWER SIZE IN NICOTIANA 373 
7. The spread of corolla limb and the length of corolla tube do not 
behave in the same manner with reference to the operation of the 
various factors which are shown to be of importance in determining 
flower size in Nicotiana. Length of corolla is more stable than spread 
of corolla, which is rather readily subject to modification under the 
stress of internal and external conditions attending development. 
8. The only true distribution representing the flower size of a 
population must be based upon measurements which, for each plant, 
extend over the greater part of the period of flowering normal for 
the given species or hybrid group or cover an identical portion of the 
flowering period of each plant. If in a large F2 hybrid population, 
some plants are measured early in the flowering season, others in the 
middle of the flowering season, and the remainder late in the flowering 
season an unusually extensive range of variation in the distribution 
resulting may be due to modifications in flowering size dependent upon 
inherent ontogenetic processes and genetically of little significance. 
University of California, 
Berkeley. 
