EXPERIMENTAL EVOLUTION. 139 



and minus ( — ) races of dicEcious species and by the fact that it has 

 given rise to another distinct mutant which does produce zygospores, 

 although in scanty amount. 



THE VASCULAR ANATOMY OF VARIANT BEAN SEEDLINGS. 



Dr. Harris has, for some years, been breeding strains of beans with 

 remarkable abnormalities that appear even in the seedling stage. Since 

 1917 a detailed study of the vascular morphology of these variant bean 

 seedlings (in comparison with the normal) has been under way in co- 

 operation with Professor E. W. Sinnott, of the Connecticut Agricultural 

 College, and with the assistance of Dr. John Y. Pennypacker and Mr. 

 G. B. Durham. A first paper, covering the problem of number and 

 variability of bundles in the different regions of dimerous and tri- 

 merous seedlings is now in press. The results of this study show that 

 external differentiation, such as that which characterizes dimerous and 

 trimerous seedlings of Phaseolus vulgaris, is accompanied by profound 

 differences in internal structm-e. They show further that anatomical 

 characters, which by morphologists in general have been regarded as 

 relativel}^ stable, may be highly variable, even in series of individuals 

 which are genetically highly homogeneous. Furthermore, the results 

 show that variability in morphological characters is not a constant for 

 the plant as a whole, but may differ from region to region or from organ 

 to organ. In the seedling types investigated, for example, hypocotyl 

 and epicotyl differ widely in the variability of bundle-number. Fur- 

 thermore, differences in variability from organ to organ or from region 

 to region are not constant, but may be conditioned by other morpho- 

 logical features. Thus, the variability of bundle-number of normal 

 seedlings is higher in the hypocotyl than in the epicotyl. In seedhngs 

 with three cotyledons and three primordial leaves just the reverse is 

 true. Other phases of the problem will be discussed in papers nearly 

 ready for publication. 



THE ORIGIN OF PIEBALD SPOTTING IN DOGS. 



During the past year Dr. Little has pubhshed a note concerning the 

 occurrence of piebald mutants in thoroughbred Scottish and Airedale 

 terriers. These two breeds have been selected for generations for ab- 

 sence of white spotting and are unknown in piebald forms. The sudden 

 appearance of spotted mutants with a considerable amount of white 

 demonstrates that in some forms at least clearly piebald forms can arise 

 without gradual selection from minute beginnings. 



ALTERATION OF THE QUALITY OF A POPULATION BY SOMATIC SELECTION. 



Dr. Banta has completed, ready for press, work upon selection for 

 reactiveness to light of Entomostraca of the order Cladocera. The 

 study has a special interest in being, apparently, the first extensive 

 investigation of selection of a purely physiological character. As 



