May 20, 1911 



HORTICULTURE 



ui 



MENDEL'S LAW AS RELATED TO 

 HEREDITY AND BREEDING. 



By Dr. llerrnuiim Decker. Translated from 

 •'Oosmus'' by LUistave Tbomineu. 



IV. 



So far, we have been considering 

 only one character at a time, in our 

 crosses. Now we will obesrve two 

 different ones at the same time. While 

 observing the working of heredity in 

 regard to height of plants, we will 

 now observe how the (_olor of the seed 

 will be affected when, for instance, we 

 cross peas again. 



Tf the color of the seed "mendels," 

 then it must do so in conformity to 

 our law. And so it does, but the thing 

 now becomes more complicated. Lft 

 us take a tall sort of peas, having 

 green seed, and cross it with a dwarf 

 one, having yellow seed. Our object 

 is to get a new sort, it to be dwarf 

 and having green seed coming true 

 from seed. We cross-fertilize, harvest 

 and sow the seed again. What we do 

 get is just the opposite from what we 

 want; these bastards of the first gen- 

 eration are all tall and yellow-seeded. 

 We might think that we had failed and 

 probably would now do the most fool- 

 ish thing, by giving up further trials, 

 so as not to waste any more valuable 

 time. Very likely we would pull up 

 the plants and be done with the use- 

 less "bastards." Of course, this would 

 be wrong, for, if we consider the re- 

 sult thus far, we should be glad, be- 

 cause, according to Mendel's law, our 

 wished for new sort MUST present 

 itself already in the next generation, 

 and, what is more, must be iiiire and 

 true to type in the seed of the following 

 genemtions. There will be no need of 

 "breeding up the type" for a number 

 of years, as heretofore. 



The result of our cross: All tall and 

 yellow-seeded, shows, that of the two 

 opposing characters, tallness, has sup- 

 pressed dwarfness and the yellow of 

 the seed has suppressed the green. If 

 we now sow these yellow seeds, (in 

 the constitution of which the disposi- 

 tions for dwarfness and for green are 

 still present) then we will get % tall 

 and 14 dwarf, also % yellow-seeded 

 and 14 green-seeded. Among every 

 sixteen of the plants there will be 

 twelve tall and tour dwarf and among 

 the twelve tall ones, nine will be yel- 

 low-seeded and three green-seeded; 

 among the four dwarfs we will have 

 three with yellow and one with green 

 seed. 



This means that among each sixteen 

 of the offspring there will appear with- 

 out fail, one plant which is dwarf and 

 has green seed — and this plant will 

 again produce seed that comes true 

 and so we have the sort we had been 

 anxious to get: Dwarf irith green seed. 



While formerly, breeders, crossing 

 at random, often had to wait years to 

 get the expected results, it is now pos- 

 sible to realize a wanted object in the 

 second generation with all the posi- 

 tiveness of success. One thing the 

 breeder must always keep in mind, he 

 must remember that the seeds which 

 he gathers after crossing, may, and 

 most always will look just alike, (in 

 the above case, yellow), but internally 

 they are not so. He must sow each of 

 these seeds by itself. 



Another example: Crossing the to- 

 mato "Fireball" red, with the yellow 

 "Queen," gave in the first generation, 

 fruit which resembled Fireball in color. 

 This is easily explained by the predom- 

 inancy of the red color. More aston- 



POLYPODIUM GLAUCUM CRISTATUM. 



This elegant new fern is well worthy 

 of a place in every collection. It is 

 entirely distinct and grows into a fine 

 specimen plaii.t, with fronds about 2 ft. 



Cottrtcsy 0/ H. A. Drefr 



high. The fronds are glaucous metal- 

 lic blue in color and as the picture 

 shows, the edges of the pinnae are 

 gracefully waved and crisped. 



ishlng is the result in the second gen- 

 eration. Here are two new colors, be- 

 side the red and the yellow we find 

 crimson and orange. How comes this 

 about? We can explain it if we take 

 into account the fact that the red of 

 the Fireball is a combination of yellow 

 in the skin and the red of the meat of 

 Fireball, while the Queen looks yellow, 

 because its skin is without color and 

 the yellow meat shows through it. So 

 here is "mendeling" of two characters: 

 First, of the red and of the yellow col- 

 or of the nleat,, second, of the yellow 

 and of the colorless skin. Because the 

 first mentioned characters suppressed 

 the others there could be, in the first 

 generation, no other fruit than: with 

 yellow skin and red meat, all resem- 

 bling Fireball. Of external resenthlanee 

 but interiorly different, because, in each 

 fruit, two characters have been sup- 

 pressed: the colorless-transparent skin 

 and the yellow meat of the Queen. But 

 already in the next generation the sup- 

 pressed characters come again. For, 

 when in fertilization, the different 

 characters contained in the gametes 

 meet each other and form all of the 

 possible sixteen combinations, then 

 there must be also such of those, in 

 which the predominant characters are 

 not present and where the suppressed 

 characters have a chance to show 

 themselves. 



This is why in crossing the two sorts 

 of tomatoes, two new sorts appear in 

 the second generation — of course as 

 pure and impure specimens. Under- 

 standing this, then it is easy to sepa- 

 rate the pure and the impure, after 

 having sowed the seeds separately. 

 The above mentioned facts were not 

 understood before Mendel's law had 

 been discovered and breeders would 

 waste years and years trying to get a 

 new sort and then getting it true to 



seed, while that very sort always ex- 

 isted already in the second generation. 

 But not realizing that the first bast- 

 ards look alike, externally, but are of 

 different dispositions, internally, breed- 

 ers would cross and recross the pure 

 with the impure, unintentionally and 

 unknowingly. If in the end the 

 looked-for object did present itself, 

 after the correct combination had been 

 accidentally stumbled upon then the 

 breeder would claim the credit for 

 •having spent years in breeding up to 

 type." 



One of the most beautiful examples, 

 where "mendeling" takes place in two 

 l)airs of characters at the same time, 

 has been shown by Correns, with corn. 

 This case is so much more interesting 

 because it shows that it is not neces- 

 sary to wait for the new plants at all; 

 the proof of "mendeling" can in this 

 instance be seen in the seed on the 

 ear of corn. 



Crossing a blue corn with a yellow 

 gives at once an ear of all blue 

 kernels. This is because blue predomi- 

 nates and at fertilization alters the 

 substance of nutrition (the endos- 

 perm). This is one character. (Nawa- 

 shin and Guignard have demonstrated 

 the above fact.) But in crossing Zea 

 Mays coeruleo dulcis, which has blue 

 wrinkled kernels with Zea alba, which 

 has white smooth kernels, we get in 

 the first generation, ears with all the 

 kernels smooth and blue. These are 

 impure of course and, crossed among 

 themselves, bring in the second gen- 

 eration ears with kernels among each 

 sixteen of which we find % blue and 

 % white — that is twelve blue and four 

 white, but also % smooth and % 

 wrinkled, a total of nine blue-smooth, 

 three v/hite-smooth, three blue-wrin- 

 kled and one white-wrinkled. This is 

 a be.iutiful, practical demonstration of 



