SPECIFICITY OF PROTEINS AND CADBOHYDRATES 
95 
By these methods physico-chemical unit-characters and unit- 
character-phases can be reduced to figures from which charts can be 
constructed which show in the case of each starch that the sum-total 
of these values is as distinctive of the kind of starch and plant source 
as are botanical characters of the plant. In determining these values 
certain precautions must sedulously be observed in order to obtain 
dependable results. Thus, in the polarization, iodine and aniline 
reactions, definite though arbitrary standards of comparison must be 
adopted. This can crudely but satisfactorily be accomplished by 
selecting as standards three or four starches which exhibit desired 
gradations of value, and constructing a scale by the aid of which 
values can be reduced in figures. In all of the gelatinization reactions 
the examinations must be made on the stage of the polarizing micro- 
scope. In determining the temperatures of gelatinization especial 
care must be exercised in regard to uniformity in the rapidity with 
which the preparations are heated, together with such other precautions 
as have been found essential in determining ''melting points." In the 
reactions with the chemical reagents it is absolutely essential that 
immediately upon the addition of the reagent to the starch on the 
slide the preparation be kept air-tight to avoid changes in concentra- 
tion of the reagent by loss or addition of water, and to avoid effects of 
oxidation. It goes without saying that in the iodine, anihne and 
chemical-reagent experiments it is necessary to use definite and 
constant proportions of reagent and starch. Finally, inasmuch as the 
starch of any given plant varies somewhat in relation to season, rest 
and activity, the part of the plant in which it is formed, etc., it ob- 
viously is important in comparative experiments such as those under 
consideration to obtain specimens from corresponding parts of plants 
and under other corresponding conditions. In the present researches 
all of the starches were prepared from bulbs, tubers, rhizomes, etc., 
in the resting state. Each preparation was obtained from a number 
of specimens, usually 25 to 50, so that each is representative of the 
plant source. 
The measure of value to be attached to the results of researches 
that are carried out along such exceptional lines, and by means of 
such seemingly gross methods of study, must naturally rest inherently 
upon the uniformity of the results of repeated experiments and upon 
the conformity of the results with established data of the systematist. 
As to the former, it need only be stated that when experiments have 
