CELL MEASUREMENT AS AN AID IN THE ANALYSIS 
OF QUANTITATIVE VARIATION* 
WiLBER BrOTHERTON, Jr., AND H. H. BaRTLETT 
The inheritance of quantitative characters is now commonly 
interpreted on a basis of multiple Mendelian factors. It is not too 
much to say, however, that relatively little has been done to identify 
these factors. Enough of them have ordinarily been postulated to 
account mathematically for the results in any given case, but a biologi- 
cal analysis has seldom been attempted. One must except the work 
of Emerson,^ who has found that the height of a bean plant is due to at 
least three, and probably more, independent factors, namely, the 
number of internodes, the length of the individual internodes, and 
the habit of growth, whether determinate or indeterminate. It has 
seemed desirable to us to proceed still further with the analysis and 
we have taken up first the problem of internode length. 
Variation in the length of an internode may be correlated either 
with variation in the number or size of the constituent cells. A priori, 
therefore, there are at least two factors whose relative importance it 
should be possible to measure in any given case. If, in addition, it 
should be possible to demonstrate the hereditary behavior of either 
factor, or of both, and to determine the fluctuations of both due to 
environment, the whole problem of the inheritance of quantitative 
characters would become much more concrete and would be brought 
correspondingly nearer to a solution. 
Before proceeding to the analysis of genetic variations, we under- 
took to test the proposed method by applying it to a variation brought 
about by environmental agencies. The etiolated epicotyl of Phaseolus 
multiflorus Willd. was chosen, because it is much longer than the normal 
epicotyl grown in light. Not only do the results demonstrate the 
feasibility of resolving internode length into less complex characters, 
but they are also of considerable interest per se, adding, as they do, to 
* Papers from the Department of Botany of the University of Michigan, no. i6i. 
1 Emerson, R. A. A genetic study of plant height in Phaseolus vulgaris. Nebr. 
Agr. Exp. Sta. Res. Bull. 7: 1-73. 1916. 
192 
