388 PROTOPLASM 



cyparissias, E. esula, E. virgata, and E. salicifolia all give migra- 

 tion curves of like form and have isoelectric points all very close 

 to pH 4.0. A second group (Fig. 165^) including E. pinea and 

 E. segetalis showed the same relationship among its members, 

 with curves and isoelectric points (pH 3.3) alike among them- 

 selves but different from those of the first group. The direction 

 of migration of all species examined was readily reversed; i.e., 

 the original sign (negative) of the charge on the particle is 

 reversed at the isoelectric point as stated in terms of a pH value. 

 The rate of migration at a definite pH value, the degree of acidity 

 at which the direction of migration changes (the isoelectric point), 

 the shape of the curves, and the relationships established on 

 these grounds all depend upon the nature of the substance that 

 coats the latex particles. This coating appears to be protein, 

 at least in some cases. In others, it is doubtful if proteins are 

 the cause of the behavior. The question as to whether the 

 specificity of the curves is due to specific chemical differences 

 in the proteins or to different proportions of the same proteins 

 composing the mixture on the surface is as yet undecided. 

 The latter surmise appears to be the more correct one. In other 

 words, whatever the coating substances may be — proteins, 

 alcohols, fatty acids, or carbohydrates — in each taxonomic 

 group of species there seems to be a definite mixture composing 

 the surface of the latex, different from that of any other species. 

 Mez appears to be dealing with qualitative differences in proteins 

 shown by reactions of families with each other but giving no 

 differences in reaction from species to species. Moyer may be 

 showing a quantitative difference which is also specific. We find, 

 therefore, that there is a definite relationship between the 

 coatings of latex particles from different species of plants which 

 is in agreement with the taxonomic relationship of the plants. 



The geographic distribution of the species is also in keeping 

 with this relationship. Thus, E. virgata, E. cyparissias, E. 

 esula, and E. salicifolia all come from central and southern 

 Europe and are closely related. Of the four, E. salicifolia 

 diverges most widely in distribution and also in the curve shape. 

 Both E. pinea and E. segetalis, with like curves and fike isoelec- 

 tric points, come from the Mediterranean region. 



Chromosome counts show an agreement between species 

 which harmonizes quite well with latex, taxonomic, and geo- 



