INTRODUCTION. 



tioiu) tli is property became fixed and the race hrcd true. 

 Similar phenomena have been recorded by other M|HTI- 

 inenter". Permanent odor hanges were induced by 

 Wolf (/.cit. f. md. Al*t. u. \ ;.. u. <IO) ii, 



u.< pruili,/iusiu by propagation m culture media 

 containing small amounts of potassium and other salts. 

 Rosenow's (Jour. Inf- 1914, xiv, 1) investi- 



gations show mutations and transformations of the strep- 

 tococcus- pneumococcus group by means of environmental 

 conditions. Thiele and Kmhleton (/.eit. f. Immunitats- 

 forseh u. ex per. Ther., I'M.!. MX. >'< I :i I brought about 

 such morphological and physiological changes as to 

 transform one species of bacillus into another. Revis 

 11, 1913, i \\x\i. 373) from an orig- 

 inal typical culture of Bacillus eoli from a single cell 

 produced two strains one of which appeared slightly 

 modified hut which could not be further altered, and 

 another which underwent profound and increasing 

 chan. ng in an organism entirely different from 



:i:iiml. the strain remaining of a permanent charac- 

 >n (1W. Nat Acad. BeL, l'M5, T, 160) in 

 cultures of Bacillus roli obtained mutation that "seenu 

 to fulfil the requirements (a) of appearing suddenly 

 without intermediate stages, (b) of being irreversible, 

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

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



I saccharose- and raffinose-fermenting power), and 

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

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

 found that metabolism was so affected in Bacillu* an- 

 lhrnci.i hy ultra-violet rays as to cause marked mutations. 



anliewitach (Zeit f. wiss. Zool.. 1878, xxv, 103; 



. in experiments with various crus- 



tacee to show effects of environment, found in Daphnia 



and Branchipu* that changes in salinity brought about 



marked functional and morphological alteration of char- 



- commonly regarded as being specific. Woltereck 



l i. deutech". zool. Gesellsch., 1000, 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 Mendclian 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 Mcndclinn 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 he made, n 

 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. In a word, it deal? 

 with hut one of several types of mechanisms of hered- 

 itv. Considerable misconception has already arisen be- 

 cause of absolutely false ideas that have been promul- 

 gated by hybridizers who have selected in their investi- 



gation* only such plants as yield offspring which in their 

 phenomena of inheritance conform to the Ifendelian 

 Law, or who have selected only such characters for 

 mation as agree with tin. law and entirely ignore 

 other* which represent non-Mendel im inheritance It 

 U obvious that in order to obtain safe results for 

 :iixl against any dix-trine it is essential that all 

 of the character*, as far as possible, should be re- 

 corded and without reference to preconceived theories or 

 hypotheses, Scarcely anything in scientific invent!;: 

 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 Mendclian phenomena is to be found in an 

 absence of a recognized and wholly satisfactory nietlxl 

 of standardization. It is obvious that until such it 

 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 DeVries (Mutation Theory, 1!>00) and by various 

 subsequent investigators. A large literature has accumu- 

 lated bearing especially upon Ornothrra and certain other 

 L'onern in which not only mutations but also spontaneous 

 hybridizations have been recorded as being of frequent 

 occurrence. Whether or not the mutants of I i.-Vrie* and 

 his school are in fact mutants or unquestionable hybrids 

 that have arisen from spontaneous crossing is a warmly 

 debated question. Bartlet (American Naturalist, 1015, 

 xi-ix, 129; Botanical Gazette, l!>ir>. MX, filO) contends 

 that there arc Omolhrra mutants; that the mutant-ratio 

 can not bo explained on Mendclian grounds ; that muta- 

 tion is a distinct process from Mendelian segregation; 

 and that the phenomena exhibited hv th<> mutants Orna- 

 thera lamarckiana. O. bifnnin, and f). prnrtinmla can not 

 be attributed to hcterozygosis. 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 *ui 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 Mendel ian conception 

 that mutation is only Mendelism under another gum. 



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. Ah 

 Vererb., 1912, TIM, 89) holds that mutants are combina- 

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

 delian characters. Renner (Flora, 191 1. < VM. 1 1", i also 

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

 delian basis. Davis (Amer. Xst, 1911, XLT, 193; ibid.. 

 1912, XLVI, 37?) found, in studies of the offspring of 

 different species of Oenothfra. thst in gross morphologi- 

 cal characters the hybrids are intermediate between the 

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

 marclciano, the best-known of all mutants. Jeffrey 



