170 BROOKLYN BOTANIC GARDEN MEMOIRS 
the line between ‘‘normal,’’ and ‘“‘abnormal”’ as applied to the dis- 
tinction between plants which have cotyledons inserted on the same 
level and those which have one of the pair sensibly higher on the axis 
than the other. “Slightly but distinctly separated,’ has been the 
descriptive term used in our classification schedules. The cotyledons 
range in position from those which are just perceptibly not inserted on 
the same level to those which are perhaps two or three or four milli- 
meters apart. So imperceptible is the line of distinction between nor- 
mal and abnormal plants that in the classification of the seedlings 
frequent discussions arose concerning the normality or abnormality of 
individual plants. 
In the present paper I am considering only the simplest type of 
abnormality. This course has been followed for two reasons. 
First, the proof of the existence of a physiological differentiation 
associated with a very slight structural variation is of far greater in- 
terest than the demonstration of measurable physiological differentia- 
tion associated with great morphological variation. Second, other 
types of abnormality with which I have dealt are so difficult to secure 
in satisfactorily large series that the number of samples as yet avail- 
able is not sufficient to justify detailed comparisons between the 
different types of abnormality. I hope ultimately to be able to meet 
these difficulties. For the present the one type of structural devia- 
tion dealt with serves to illustrate the method and one phase of the 
results of the investigations. : 
PRESENTATION OF DATA 
Consider first of all the green weight of the organs selected. 
The average green weight of the primordial and of the first com- 
pound leaves for plants which are normal except for slight separation 
of their cotyledons is shown in Table I. 
With one single exception, the average weight of the primordial 
leaves of the normal plants is higher than that of the abnormal plants. — 
In the single exception to the rule, the difference is small in amount. 
The average weight of the first compound leaf produced by abnormal 
plants of this class is in every case but one lower than the weight 
produced by the sensibly normal individuals. The exception to the 
rule is the same sample as in the case of the primordial leaves. 
The average weight of primordial leaf tissue in the abnormal plants 
is .5873, the average weight for normal plants is .6680, and the average 
difference —.0807. The differences in mean weights range in the 
individual samples from +.0074 to —.1286. For the first compound 
leaf of the same plants the average weight of the tissues from abnormal 
individuals is .4797, from a normal plant it is .5610, while the average 
