October 29, 1915] 



SCIENCE 



623 



Mutations, or discontinuous variations, belong 

 in the first class, and they are of many kinds, dif- 

 fering in their manner of origin and their manner 

 of inheritance. Studies of the cell structure of 

 mutants has made it possible to classify mutations 

 into (1) those which are fundamentally morpho- 

 logical and (2) those which are primarily chem- 

 ical. The hypothesis that each Mendelian charac- 

 ter is the result of a chemical change in the na- 

 ture of one chromosome in a germ cell, will ac- 

 count for not only the origin, but also the in- 

 heritance of every simple Mendelian character. 

 Such a mutation is no more unlikely than muta- 

 tions in bacteria, many of which are now known 

 to occur. Each Mendelian pair of characters 

 therefore represents a mutation which has occurred 

 in past time. 



The morphological mutations at present known 

 consist in changes in the number of chromosomes 

 in cell nuclei. The fundamental chromosome num- 

 ber in the genus (Enothera is 14, but CE. lata has 

 15, cm. gigas 28, etc. In these oases there has been 

 a change in the constitution of the nucleus which 

 may be considered to be morphological in nature. 

 The change is propagated to every part of the 

 organism by mitosis or cell division. Hence, for 

 example, every cell of (E. lata has 15 chromosomes, 

 and the peculiarities of OH. lata appear to result 

 from this fact. One may conclude that each mu- 

 tation, in plants at least, is a cell change origi- 

 nating in a particular germ cell and represented 

 in every cell of the adult mutant organism. 



The Idea of Multiple Causes as applied to Evo- 

 lution: Wm. E. Eitter, Scripps Institute for 

 Biological Eesearch, La Jolla, California. 

 To be published later. 



Seventeen Years' Selection of a Character Show- 

 ing Mendelian Inheritance: Eatmond Peakl, 

 Maine Agricultural Experiment Station, Orono 

 (read by title). 



Are there such Things as Unit Characters? S. J. 



Holmes, University of California. 



The doctrine that organisms are mosaics of in- 

 dependently varying elements is one that has fig- 

 ured largely in biological speculation from Dar- 

 win's time to the present. It is very intimately 

 associated with many problems of heredity and 

 evolution, and one is very liable to think in terms 

 of the doctrine and unconsciously allow it to shape 

 his opinions even though he may not avow his 

 adherence to it. The doctrine is founded on the 

 assumed independent variability of parts and the 

 independent transmission of so-called characters. 



Many facts pointing to independent variability 

 have been amassed by Darwin, De Vries and Weis- 

 mann, and the latter has argued with especial 

 force that it is impossible for several organs to be 

 simultaneously perfected unless variations in the 

 one occur independently of variations in the others. 

 On the other hand, it may be pointed out that nu- 

 merous variations have far-reaching correlations 

 and that often a variation may be particularly 

 manifest in some one feature, but nevertheless be 

 the result of a general organic change which is 

 only obscurely expressed in other parts of the or- 

 ganisms. 



Mendelian inheritance which seems to lend sup- 

 port to the conception of the organism as a mosaic 

 product is open to a quite different interpretation 

 if we assume that what are segregated are not the 

 bearers of unit characters merely, but the hered- 

 itary bases of organisms as wholes having this or 

 that peculiarity. The bearing of the mosaic and 

 organismal standpoints on various questions of 

 evolutionary theory can be brought out only in 

 the fuller paper of which this is a brief abstract. 

 Adaptation as a Process: Habry Beal Torret, 



Reed College, Portland. 



Some Genetic Studies of Several Geographical 

 Baces of California Veer Mice (projection of 

 autochromes, with demonstrations and illustra- 

 tions) : F. B. Sumner, Scripps Institute for 

 Biological Eesearch, La Jolla, California. 

 Mice of the species Feromyscus maniculatus 

 were collected in four regions of California, rang- 

 ing climatically from the Mojave Desert to the 

 humid northwest coast (Eureka). Fourteen char- 

 acters of these mice have been measured, and the 

 results subjected to statistical analysis. In gen- 

 eral, the Eureka form (ruhidus) differs more 

 widely from the other three races than these do 

 from one another, and hybridization has not thus 

 far succeeded with it. Buhidus exceeds the others 

 conspicuously in length of tail and foot, and to 

 some extent in skull length and cranial capacity, 

 comparison being made between animals of equal 

 body length. This subspecies is also the darkest 

 of the series. The increase in pigmentation, cor- 

 relatively with increase in humidity, is a well- 

 known principle to which these mice conform, but 

 the increase in the length of the appendages 

 toward the north (shown in ruiidus and still more 

 evident in Alaskan races) stands in contradiction 

 to another well-known generalization, and is hard 

 to reconcile with experimental evidence. 



The subspecies gamheli from Berkeley or La 



