676 



HORTICULTURE, 



May 26, 1906 



Theories and Facts in Plant Breeding 



In the issue of Horticulture for April 51st, 1906, 

 there is an article entitled "The Keal Inwardness of 

 Hybridizing," by N. B. White. This contains many 

 statements which are very loose and very inaccurate, 

 especially for one, who, avowedly, by word and by title, 

 gives the impression that he is stating the scientist's 

 point of view. Not only this, but the article summarizes 

 two laws in a manner both absurd and incorrect. These 

 laws have been deduced from recorded experiments, care- 

 fully tabulated and studied; they have been given out 

 by biologists as attempts at expressing the truth, and as 

 attempts "to declare the course of heredity under given 

 conditions." They are interesting, historically as 

 showing the development of methods, work and theories; 

 they are useful practically in direct proportion as they 

 enable us to predict of our attempt at hybridizing and 

 cross-breeding. 



The Galton law. amended by Pearson, is of little 

 value to practical men and is somewhat as crudely 

 stated by Mr. White. The Mendel law promises to be 

 of great value, though still under heavy fire of discus- 

 sion and experiment and an absolutely definite state- 

 ment that it "is a great boon to breeders" can not be 

 safely made now. However, these experiments are 

 giving much which in time may prove the law to be 

 the great desideratum for which we are all seeking. 



In 1901, in its Journal The Royal Horticultural 

 Society of England published a translation of Mendel's 

 own paper describing his experiments. This was made 

 by Professor \Y. Bateson of Cambridge University and 

 is, so far as I know, the first publication of this paper 

 in English. Nowhere in this or in subsequent papers 

 could any statements be found which would lead to 

 such a change of breed in poultry as Mr. White 

 describes, nor could Mendel find in this description any 

 trace of his theory. Mr. White in his version of Men- 

 del's law supposes "the purity of parents, hence, the 

 purity of germ cells." Does it take a law deduced by 

 hard labor, both mental and physical, as Mendel's law 

 was, to predict that if two pure individuals be bred 

 together their offspring will be pure? How could it 

 be otherwise. Such a statement is adding insult to 

 injury. The conception of "the purity of parents" is 

 not only untenable but unthinkable, unless we throw 

 away our basal theory of evolution and accept that of 

 special creation, when, I grant, the individuals, fresh 

 from the workshop of the creator would be pure. But 

 in how few generations would such a mixture come into 

 existence as would make Mr. White's head swim. 



Mendel experimented on a number of varieties of 

 plants, chosing those characters which contrasted 

 markedly and which could not be open to questions 

 when results were to be given out, and which could be 

 readilv recognized. By common consent those experi- 

 ments on the ordinary garden pea have become classic. 

 In the tabulation of the results of his experiments. Men- 

 del found that there was a marked difference in the 

 inheritance of two contrasting characters, in a definite 

 number of experiment- each appeared in a definite pro- 

 portion and ratio. That character which appeared the 

 more often was called a "dominant character," that 



appearing less often was called a "recessive character"' 

 and together we have deduced the conception of "unit 

 character." Selecting at random three of Mendel's own 

 illustrations from his pea experiments we have: 



1. The shape of the ripe seed, whether round and 

 smooth or angular and wrinkled. 



2. Shape of the seed pod, whether simply inflated or 

 deeply constricted between the seeds. 



.'!. Length of stem, whether the plant is giant or 

 dwarf. 



The tabulations show that the round smooth seeds, 

 the simply inflated pods and the giant stems are the 

 dominant characters of these three pairs of Mendelian 

 characters. The dominants and recessives appear in 

 the proportion of 3:1. This is the first tenet of Men- 

 del's law ; the second is that the germ cell is pure, that 

 is that it carries either the dominant or recessive char- 

 acter of any given pair of contrasted characters, but 

 never both, a perfectly tenable and thinkable position, 

 for a pea could not be both smooth and wrinkled, its 

 pod could not be both inflated and constricted nor 

 could its stem be both dwarf and giant. 



The following statement of the law is Mr. Bateson's; 

 it is not rough and it has one strong recommendation, 

 Mendel would recognize it if lie were to read it. It is 

 taken from the Royal Horticultural Society's Journal, 

 already referred to. "The conclusion which stands out 

 as the chief result of Mendel's admirable experiments 

 is of course the proof that in respect of certain pairs of 

 differentiating characters the germ cells of a hybrid or 

 cross bred are pure, being carriers and transmitters of 

 either one character or other, not both. That he suc- 

 ceeded in demonstrating this law for simple cases with 

 which he worked it is scarcely possible to doubt. 



"In so far as Mendel's law applies, therefore, the con- 

 clusion is forced upon us that a living organism is a 

 complex of characters, of which some, at least, are dis- 

 sociable and are capable of being replaced by others. We 

 thus reach the conception of unit characters, which may 

 be rearranged in the formation of the reproductive 

 cells." 



It will indeed be the millennium when we can analyze 

 the pollen cells and the ovules and read their characters, 

 that will be of vast help to practical plant breeders, for 

 of course, we will then be able to revitalize these 

 sources of life after we have killed and fixed them pre- 

 paratory to our examination ; and then, each and every 

 other pollen grain or ovule will carry with it its own 

 recommendation. Let us hope that they will be more 

 truthful than the majority of recommendations which 

 one gets. Let Mr. White examine a little into the 

 intricacies of these cells which he so glibly plans to read 

 as a phrenologist reads one's head and discover how 

 difficult it is to understand in a small measure the plain 

 physical -tincture and how many years and how much 

 labor have been spent upon gaining the small store of 

 knowledge we now have in this direction. 



The closing statement is a marvellous finale to Mr. 

 White's article. I would ask him to compare it with 

 his opening statements, and then tell me what its 

 point is. 



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