IN ri;<>i)UCTION. 



19 



tions) this property became fixed and bred true. 



Similar phenomena have been recorded by other experi- 

 menters. Permanent color changes were induced 1>\ 

 Wolf (Zeit. f. in.l. Abst. a. Vererb., L909, n. 90) in 

 igiosus by propagation In culture media 

 containing small amounts of potassium and other salts. 

 Rosenow's (Jour. Infect. Dis., 1914, \iv. t) in 

 gations show m ut a tii ms and transformations of the stri p 



tococcus-pneitniococriis group by means of em ir nental 



conditions. Thiele and Embleton (Zeit. E. trnmui 

 Eorech u. exper. Ther., L913, six, 643) broughl aboul 

 such morphological and physiological changes ae to 

 transform one species of bacillus into another. K< 

 (Proc. Roy. Soe., B, 1913, t.xxxvt. 373) from an 

 inal typical culture of Bacillus coli from a single cell 

 produced two strains one of which appeared slightly 

 modified but which could not he 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. Nat. Acad. Sci., L915, i. ICO) in 

 cultures of Bacilli/* call obtained mutation that "scni- 

 to fulfil the requirements (a) of appearing suddenly 

 without intermediate stages, (h) of being irreversible, 

 at least for three years and for some hundreds of test 

 tube generations, (c) of comprising change in twocl 

 bers (saccharose- and ramnose-fermenting power), and 

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

 Henri (Compt. rend. Acad. Sci.. 1914, CLVTII, 1032) 

 found that metabolism was so affected in Bacillus an- 

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

 Schmankewitsch (Zeit. f. wiss. Zool., L875, xxv, 103: 

 I s "'. win. 129), in experiments with various crus 

 tacese to show effects of environment, found in Daphnia 

 and Branchipus that changes in salinity broughl about 

 marked functional and morphological alteration of char- 

 acter; commonly regarded as being specific. Woltereek 

 (Verh. deutsch. zool. Oesellsch., 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 fixitv 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 cond I if 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 as, and never can be made, a 

 universal principle of heredity, and that the main ques- 

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

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

 with but one of several types of mechanisms of b 

 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- 



ng only such plants as yield offspring which in 

 phenomena of inhi to lelian 



Law. or who have I only such character* 



examination a ith this law and entin 



others which represent uon-Mendelian inheritance. It 

 is obvious that in order to obtain safe n 

 and againsi anj doctrine it is essential that all 

 of th as far as possible, should be re- 



i ami without reference to preconceived theorii 

 Scarcely anything in Bcientifii 

 can be moi than an attempt tn make 



lit theory, hypi ■trine, and to ignore them 



if they do aot. One of the man i 

 studies of Mendelian phenomena is to be found in an 

 absence of 8 aized and wholly satisfactory mi 



of standardization. It is obvious that until sui 

 adopted the * •■ tent of applicability of the Mendelian 

 trine to the explanation of phenomena of heredity i 

 remain in considerable doubt. 



Anion- the fundamentally important contributions 

 to the study of ' pertaining to mutations 



by" DeVries (Mutation Theory, 1909) and by various 

 subsequent investigators. A large literature has accumu- 

 lated bearing especially upon I 1 certain i 

 genera in which not only mutations hut also -pontaneous 

 hybridizations have been recorded as being of frequent 

 occurrence. Whether or not the mutants of DeVrii - 

 his school are in fact mutants or unquestionable hybrids 

 that have arisen from spontaneous cro a warmly 

 debated question. Bartlel (American Naturalist, 1915, 

 xi.ix. 129; Botanical Gazette, L915, i.t\, 810) conl 

 thai there are Oenothera mutants; that the mutant-ratio 

 can not be explained on Mendelian ground-; that muta- 

 tion is a distinct process from Mendelian segregation; 

 and thai the phenomena exhibited by the mutants 

 thera lamarchiana, ' '. bii nnis, and 0. prat ! n not 

 be attributed to heterozygosis. I The Mutation 

 Factor in Evolution, 19lo) holds the new 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 arc completely inherited in some or all 

 of the offspring; and that cytologioal evidence is in 

 accord with theoretical requirements and experimental 

 ■ ts in serving to controvert the Mendelian conception 

 that mutation is only Mendelism under another guise. 



On the other hand, the hybrid and Men, lelian charac- 

 ters of mutants have led many to believe that many 

 mutants are hybrids. Heribert-Nilsson (7 " Sdbst. u. 

 Vererb., 101?, viii. SO) holds that mutants aTe combina- 

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

 delian characters. Kenner (Flora, 1014, cvit. 115) also 

 bhat DeVries's mutations are explicable on a Men- 

 delian basis. Davis (Amer. Nat., 1911. XXV, 103; ibid., 

 I'M.'. M.vt, 377) found, in studies of the offspring of 

 different spe< ies of "• n ;; , ••■>. that in gross morphologi- 

 cal characters the hybrids are intermediate between the 

 parents and that some of the hybrids resemble O. !a- 

 marckwna, the In D of all mutants. Jeffrey 



