INTRODUCTION. 



19 



tions) this property became fixed and the race bred true. 

 Similar phenomena have been recorded by other experi- 

 menters. Permanent color changes were induced by 

 Wolf (Zeit. f. ind. Abst. u. Vererb., 1909, ii, 90) in 

 Bacillus prodigiosus by propagation in culture media 

 containing small amounts of potassium and other salts. 

 Eosenow's (Jour. Infect. Dis., 1914, xiv, 1) investi- 

 gations show mutations and transformations of the strep- 

 tococcus-pneumococcus group by means of environmental 

 conditions. Thiele and Embleton (Zeit. f. Immunitats- 

 forsch u. exper. Ther., 1913, xix, 643) brought about 

 such morphological and physiological changes as to 

 transform one species of bacillus into another. Revis 

 (Proc. Eoy. Soc, B, 1913, lxxxvi, 373) from an orig- 

 inal typical culture of Bacillus coU from a single cell 

 produced two strains one of which appeared slightly 

 modified but which could not be further altered, and 

 another which underwent profound and increasing 

 change, resulting in an organism entirely different from 

 the original, the strain remaining of a permanent charac- 

 ter. Jordon (Proc. N*at. Acad. Sei., 1915, i, 160) in 

 cultures of Bacillus coU obtained mutation that " Seems 

 to fulfil the requirements (a) of appearing suddenly 

 without intermediate stages, (6) of being irreversible, 

 at least for three years and for some hundreds of test- 

 tube generations, (c) of comprising change in two charac- 

 ters (saccharose- and raffinose-fermenting power), and 

 (d) of not involving all the cells of the parent strain." 

 Henri (Compt. rend. Acad. Sci., 1914, clviii, 1033) 

 found that metabolism was so affected in Bacillus an- 

 thracis by ultra-violet rays as to cause marked mutations. 

 Sohmankewitsch (Zeit. f . wlss. Zool., 1875, xxv, 103 ; 

 1877, XXIX, 439), in experiments with various crus- 

 tacese to show effects of environment, found in Daphnia 

 and Branchipus that changes in salinity brought about 

 marked functional and morphological alteration of char- 

 acters commonly regarded as being specific. Woltereck 

 (Verb, deutsch. zool. Gesellsch., 1909, 110) recorded 

 variations in Daphnia that are heritable, and states that 

 by selection a modified race can be bred. Literature 

 such as the foregoing is plentiful, both as to plant and 

 animal life. 



The Mendelian doctrine is one of fixity and constancy 

 of characters which segregate in inheritance — ^the very 

 antithesis of what must be recognized as one of the most 

 fundamental principles of evolution, i.e., plasticity and 

 adaptability to environmental conditions that permit 

 or lead to the formation of new characters. It is im- 

 portant to note that while the Mendelian doctrine is a 

 scientific fact and of unquestionable value in explaining 

 certain phenomena of inheritance, it is also obvious that 

 it can not be accepted ajs, and never can be made, a 

 universal principle of heredity, aud that the main ques- 

 tion pertaining to this doctrine is in regard to the con- 

 ditions under which it holds good. In a word, it deals 

 with but one of several types of mechanisms of hered- 

 ity. Considerable misconception has already arisen be- 

 cause of absolutely false ideas that have been promul- 

 gated by hybridizers who have selected in their investi- 



gations only such plants as yield offspring which in their 

 phenomena of inheritance conform to the Mendelian 

 Law, or who have selected only such characters for 

 examination as agree with this law and entirely ignore 

 others which represent non-Mendelian inheritance. It 

 is obvious that in order to obtain safe results for 

 and against any doctrine it is essential that all 

 of the characters, as far as possible, should be re- 

 corded and without reference to preconceived theories or 

 h3rpotheses. Scarcely anything in scientific investigation 

 can be more pernicious than an attempt to make facts 

 fit theory, hypothesis, or doctrine, and to ignore them 

 if they do not. One of the manifest weaknesses of 

 studies of Mendelian phenomena is to be found in an 

 absence of a recognized and wholly satisfactory method 

 of standardization. It is obvious that until such is 

 adopted the extent of applicability of the Mendelian doc- 

 trine to the explanation of phenomena of heredity must 

 remain in considerable doubt. 



Among the fundamentally important contributions 

 to the study of heredity are those pertaining to mutations 

 by DeYries (Mutation Theory, 1909) and by various 

 subsequent investigators. A large literature has accumu- 

 lated bearing especially upon Oenothera and certain other 

 genera in wihieh not only mutations but also spontaneous 

 hybridizations have been recorded as being of frequent 

 occurrence. Whether or not the mutants of DeVries and 

 his school are in fact mutants or unquestionable hybrids 

 that have arisen from spontaneous crossing is a warmly 

 debated question. Bartlet (American Naturalist, 1915, 

 XLix, 139; Botanical Gazette, 1915, lix, 810) contends 

 that there are Oenothera mutants ; that the mutant-ratio 

 can not be explained on Mendelian grounds ; that muta- 

 tion is a distinct process from Mendelian segregation; 

 and that the phenomena exhibited by the mutants Oeno- 

 thera lamarcJciana, 0. iiennis, and 0. practincola can not 

 be attributed to heterozygosis. Gates (The Mutation 

 Factor in Evolution, 1915) holds the view that mutations 

 are not merely manifestations of some type of heredi- 

 tary behavior, but a process sui generis; that mutation 

 phenomena represent a well-defined type of variability ; 

 that mutations are completely inherited in some or all 

 of the offspring; and that cytological evidence is in 

 accord with theoretical requirements and experimental 

 facts in serving to controvert the Mendelian conception 

 that mutation is only Mendelism under another guise. 



On the other hand, the hybrid and Mendelian charac- 

 ters of mutants have led many to believe that many 

 mutants are hybrids. Heribert-Nilsson (Zeit. f. Abst. u. 

 Vererb., 1918, viii, 89) holds that mutants are combina- 

 tions, i.e., they represent new combinations of Men- 

 delian characters. Renner (Flora, 1914, cvii, 115) also 

 holds iihat DeVries's mutations are explicable on a Men- 

 delian basis. Davis (Amer. Nat., 1911, xlv, 193; ibid., 

 1913, XLVI, 377) found, in studies of the offspring of 

 different species of Oenothera, that in gross morphologi- 

 cal characters the hybrids are intermediate between the 

 parents and that some of the hybrids resemble 0. la- 

 marckiana, the best-known of all mutants. Jeffrey 



