May 13, 1911 



horticulture: 



705 



MENDEL'S LAW AS RELATED TO 

 HEREDITY AND BREEDING. 



By Dr. Herrmann Decker. Translated from 

 "Cosmcs" by Gustave Thommen. 

 III. 

 But how about this remarkable pro- 

 portion of numbers in the second gen- 

 eration, this ever recurring formula of 

 3:1? The answer is very simple, as 

 we shall see. To illustrate: If we 

 should cross a black guinea pig with 

 a white one, we would have repre- 

 sented the two colors black and white 

 as the color characters, of which, as 

 the result of the cross would show us, 

 the black was predominating. So ac- 

 cording to Mendel all the young would 

 be black; the white is suppressed, but 

 not lost. 



EiVery living being is the outcome 

 of the union of one male cell with 

 one female eggcell. Heredity is de- 

 pendent upon these sexual cells, 

 "GAMETES," and only what is con- 

 tained in these cells can be inher- 

 ited; the gametes of the black father 

 contained the disposition for "black" 

 only, those of the mother for "white" 

 only. 



Let these different sexual cells now 

 be represented by slips of glass, black 

 ones and plain ones. Uniting two of 

 these will give us: black-plain, which, 

 looked at, shows to our eyes "black." 

 So, also is our first generation of 

 guinea pigs black; the white of one of 

 the parents is there, but it is sup- 

 pressed or covered up by the predom- 

 inating black of the other parent. 



Now what will happen if we cross 

 these bastards? What sort of gametes 

 has the male and what sort has the 

 female? Mendel says: The gametes 

 can contain the foundation of one 

 character only. But the bastards have 

 in their bodily cells, the black of the 

 father, as well as the white of the 

 mother (the latter suppressed), conse- 

 quently, in the formation of the 

 gametes of these bastards, the two 

 characters are separated again; the 

 male forms gametes containing either 

 the "black" or the "white," the fe- 

 male foi-ms eggcells which contain the 

 disposition for one or the other color 

 alone also. 



Representing the gametes by the 

 slips of glass, we see that the male 

 forms white ones and black ones, 

 0000»»«». the female forms 

 egg cells in the same way, O O O O 

 • • • •. 



Now, any one of the black, male 

 slips may be united with either a 

 black • or a plain O female slip and 

 any one of the plain O male slips may 

 unite with a black • or plain O female 

 slip. 



This will give us the following four 

 combinations (other combinations are 

 not possible), • X •, • X O, O X •, 

 O X O. We have now four pairs of 

 slips, of which three pairs show black 

 and one pair which shows plain, O x 

 O. But of the three black pairs only 

 one is pure black, • x •, two pairs 

 are impure, because each pair con- 

 tains one plain slip, • x O, O x •. 

 The fourth pair is pure plain, O x O. 

 It we should divide up the slips and 

 put them in two boxes, into one box 

 those of the male. ••••000 O, 

 and into the other box those of the 

 female, ••••OOOO, and should 

 now, blindfolded, take one slip from 

 each box at a time, to form a pair, we 

 could form no other combinations. 

 This is why in the second genera- 



tion of our guinea pigs, three of the 

 litter are black and one is white, or 

 should there be eight to a litter, six 

 black and two white. Of these six 

 black ones, two are pure black and, 

 crossed among themselves, will pro- 

 duce pure black again. The other 

 four are bastards (with the white in 

 them, but not showing, because it is 

 covered by the black) which, crossed 

 among themselves, will again throw 

 three blacks and one white. The 

 white one is pure. 



That in the impure bastard, the dispo- 

 sitions governing the foundation of the 

 characters, separate again, is the 



SECOND LAW OF MENDEL. 



Considering, how easily this law is 



Cross of the unbanded 



gives to purity of type a specific meaning. 



The eminent botanist, De Vries, has 

 coined the words "to mendel" and 

 "raendeling." These words, on ac- 

 count of their directness, have be- 

 come very popular. Any quality or 

 character "mendels." when in breed- 

 ing it combines with another similar 

 character according to Mendel's law 

 and separates from it again. Such 

 "mendeling" character - pairs, have 

 through extended experiments been 

 found in a large number. 



So "mendels" for instance: the ser- 

 ration and form of many sorts of 

 leaves. This can plainly be seen in 

 crossing the plain-leaved Urtica Do- 

 dartii with the tooth-leaved U. piluli- 

 fera. 



with the 5 banded variety of 

 Tachea Hortensis 



r r r r 



r r r r 



m 



(^ (^ % 



S © ® 

 © ^ d 



[ denotes that one character is suppressed. 



demonstrated with our slips of glass, 

 we might almost become sceptical as 

 to whether any such simple law can 

 really explain the often seemingly very 

 complicated conditions under which 

 heredity is many times displayed. But 

 numberless experiments, made by 

 many of the foremost investigators, 

 have proven the absolute correctness 

 of Mendel's laws. 



Mendel says: When the disposition 

 for one of the characters which is 

 present in the one parent, meets, in 

 crossbreeding, another of the same 

 character, in the other parent, then 

 one of the two will suppress the 

 other and predominate in the off- 

 spring. 



Crossing a red-flowered pea with a 

 white-flowered one, will give seed pro- 

 ducing red-flowering peas only; the 

 red suppresses the white totally, but 

 the second generation brings again 

 one white to each three red peas. In 

 cross breeding two specimens which 

 differ in their characters, we can of 

 course at the start not know which 

 of the characters will predominate. 

 We can realize this only by observing 

 the result of the cross. But having 

 noticed this fact in the first genera- 

 tion, puts us in a position where we 

 can force nature to confii-m and cor- 

 roborate our surmises, through the 

 second generation. 



As the astronomer is able to chart 

 the path of a planet (knowing orig- 

 inally only a fraction thereof and com- 

 puting from this) and to predict how 

 this planet will travel eternally, so 

 can now the breeder, by close obser- 

 vation of the bastards from his 

 crosses, predict which qualities and 

 characters of the parents can be 

 transmitted and fixed in the progeny, 

 according to nature's law of heredity. 

 This is a tremendous gain, because it 



Professor Arnold Lang of Zurich, 

 has made exceedingly careful and 

 painstaking experiments in crossing 

 the unbanded garden snail (Tachea 

 hortensis, with its five-banded varie- 

 ty). He proved that the five-banded- 

 ness is suppressed, in exact accord- 

 ance with Mendel's law. (Illustration 

 from photographs.) 



* A " 



"Mendeling" can take place in the 

 color of flowers and fruits, of feathers 

 of birds and coats of animals, of de- 

 signs in wings of butterflies or 

 petals of flowers, in the form of 

 leaves, and arrangement of spines 

 and thorns of fruits and plants; in the 

 size, shape or presence of horns in 

 animals, form of combs in fowls, etc. 

 Also, many qualities and characters 

 which do not strike the eye so vividly, 

 obey Mendel's law. Earliness and 

 lateness of ripening, immunity to dis- 

 ease in animals or rust in plants, fol- 

 low the same rules. Many varieties 

 of wheat are sub.iect to rust. In 

 crossing these with varieties which 

 are immune it was found that immuni- 

 ty is suppressed. Letting self-fertiliza- 

 tion take place in the bastards, gave 

 in the second generation, plants which 



