. Contributions from the Botanical Laboratory, vol. 11. Botany; Botany. 298 AMERICAN JOURNAL OF BOTANY [Vol. 21, June, 1934I MOYER EUPHORBIA 299 the velocity approaches zero. To avoid this, readings were made at small increments of pH, above and below the isoelectric point, until two suspen- sions were found having approximately equal and opposite velocities at very close pH values. These values were then reduced to terms of hydrogen- ion concentration, averaged, and re-converted to pH units. It was found that these values and the points at which the curves changed their sign (when interpolate
. Contributions from the Botanical Laboratory, vol. 11. Botany; Botany. 298 AMERICAN JOURNAL OF BOTANY [Vol. 21, June, 1934I MOYER EUPHORBIA 299 the velocity approaches zero. To avoid this, readings were made at small increments of pH, above and below the isoelectric point, until two suspen- sions were found having approximately equal and opposite velocities at very close pH values. These values were then reduced to terms of hydrogen- ion concentration, averaged, and re-converted to pH units. It was found that these values and the points at which the curves changed their sign (when interpolated) checked closely. In discussing results the abbreviation LP. will be used for isoelectric point. All the plants were tested by the ninhydrin and xanthoproteic reactions (Morrow, 1927) in the hope that these might afford a qualitative test for proteins. Other tests were not used because of possible disturbing factors in the latex. Of these two, the ninhydrin is thought to be of more value. Because of the small quantities of latex available, other, more accurate tests could not be applied. RESULTS Unfortunately, there is no recent general treatise on the species of Eu- phorbia. The monographs of Boissier (1866) and Berger (1907) are still the standard works in the field. Boissier systematizes the species by their seed and flower characters instead of their vegetative organs which, for convenience, are used by most other authors. Hence, Boissier's treatment probably represents a nearly natural grouping. His arrangement and key to the sub-groups will be followed closely in the discussion of the results of these electrophoretic experiments. For the section Diacanthium, Berger's classification will be used. Certain species represent the sole examples stud- ied in their group due to a lack of available material. Other groups are bet- ter represented, and from these comparative data could be secured. It might be mentioned that all plants investigated gave a blue color with guaiacum,
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