ELECTROKINETICS 



387 



value; this can be changed to the acid or alkahne side by the 

 use of buffers. The curves of a number of species of Euphorbia 

 show a remarkable relationship. Those species known to be 

 taxonomically related (as established by the time-honored 

 methods of plant classification) yielded cataphoretic migration 

 curves of identical form which crossed the line of no migration at 

 almost precisely the same pH value, i.e., they had the same 



Fig. \QbB.— {Continued.) 



isoelectric points; while those species taxonomically not closely 

 related yielded curves of different form, with other isoelectric 

 points. An occasional species, which did not fall into any one 

 group, proved to be an isolated form of questionable relationship 

 on taxonomic grounds. Further study brought other interesting 

 facts to light. The geographic distribution of the species was 

 such as to agree with the protein relationship, and chromosome 

 numbers showed similar conformity (though here the problem 

 is a more involved one). If we analyze a group of curves 

 (Fig. 165A), we find that the closely related species Euphorbia 



