CHAPTER I. 



INTRODUCTION. 



1. OBJECTS OF THIS KESEAECH. 



In both of the preceding researches satisfactory evi- 

 dence was recorded to justify the conclusion that com- 

 plex organic substances exist in different stereoisomeric 

 forms in different organisms, and that the differences 

 are specific in relation to genera, species, and varieties, 

 and in general in striking accord with the accepted data 

 of the systematist. Naturally it seemed to be a matter 

 of the greatest fundamental importance to determine 

 to what recognizable degree these physico-chemical prop- 

 erties are transmitted from seed and pollen parents in 

 altered or unaltered form in the hybrid; if it is possible 

 to predict the heritability of this or that property; 

 whether or not new physico-chemical properties appear 

 in the hybrid ; and if the phenomena of physico-chemical 

 inheritance are not only consistent with but also in ex- 

 planation of the data of the systematist and with the 

 experience of the plant breeder. 



2. CRITERIA OF HYBRIDS AND MUTANTS. 

 A FOREWORD. 



Beginning with the elementary investigations of 

 Linnaeus, data pertaining to the comparative peculiari- 

 ties of parents and of hybrids have been accumulating, 

 and at present, notwithstanding that thousands of such 

 sets are known in literature, only very few of them have 

 been recorded in a way that renders them of more than 

 general value in formulating laws of inheritance. Stand- 

 ards for the recognition of hybrids and mutants, respec- 

 tively, have found widespread acceptance, yet one may 

 well hesitate to inquire if in the restrictedness of our 

 analyses and comparisons, the narrowness of our con- 

 ceptions, and the manifest prejudices and errors of judg- 

 ment we have not been fostering many views that have 

 led to general misunderstanding and illusory conclusions. 



The universally recognized primary or essential dis- 

 tinguishing characters of hybrids are: Intermediateness 

 of the first generation; lessened vitality that may be 

 expressed in many ways; partial or complete sterility, 

 especially as regards the pollen ; instability and Mende- 

 lian inheritance in the second and succeeding generations. 

 But if we were to carefully examine a large number of 

 diversified characters of say a dozen hybrids selected at 

 random, what percentage of these characters would be 

 found to be intermediate, and what percentages of these 

 intermediate characters would be of mid-intermediate 

 value or nearly the same as in one or the other parent? 

 Are there not many hybrids that are nearly or quite as 



fertile as their parents, or if their fertility is subnormal 

 in the first generation may it not become normal during 

 subsequent generations? Are there not many hybrids 

 that show little or no tendency toward Mendelian in- 

 heritance, or which, in other words, breed true? Is it 

 not common to find in hybrids unimpaired vitality and a 

 luxuriance of growth even exceeding that of the parents ? 

 The primary or essential distinguishing character- 

 istics of mutants are set forth in the laws formulated 

 by DeVries: 



(1) New elementary species arise suddenly, without 

 transitional forms. 



(2) New elementary species are, as a rule, absolutely 

 constant from the moment they arise. 



(3) Most of the new forms that have appeared are 

 elementary species, and not varieties in the strict sense 

 of the term. 



(4) New elementary species appear in large num- 

 bers at the same time or at any rate during the same 

 period. 



(5) The new characters have nothing to do with 

 individual variability. 



(6) The mutations, to which the origin of new 

 elementary species is due, appear to be indefinite, that 

 is to say, the changes may affect all organs and seem to 

 take place in almost every conceivable direction. 



Do not all of these laws conform in all essential re- 

 spects with the data in many hybrids? Is not partial 

 or complete sterility common among mutants? Do not 

 mutants when crossed give rise as commonly as hybrids 

 to offspring which exhibit Mendelian phenomena? In 

 a word, has a definite line of demarcation been established 

 between hybrids and mutants ? In the present research 

 mutants, as such, are of only indirect interest, but if they 

 are hybrids, as is held by many, they are obviously of 

 direct and fundamental importance. 



One need not turn many pages of the vast literature 

 of heredity before becoming bewildered by the conflicting 

 statements of recognized authorities and noting that 

 many of even the more important deductions rest upon 

 false premises. In the following elementary sketch the 

 botanist, zoologist, evolutionist, and others who are very 

 familiar with the subject of heredity will not find any- 

 thing new, either in facts or deductions, the sole purpose 

 of the presentation being to lay before the general reader 

 data to show the antipodal views of different authori- 

 ties ; to indicate with what reserve we should accept cer- 

 tain well-known laws, rules, criteria, and conceptions; 

 and to point to what should, in a general sense, be ex- 

 pected in heredity upon the bases of recognized facts of 

 hybridization and mutation. 



