272 



The Journal of Heredity 



parents. This one is shortly followed 

 by others from the side shoots. These 

 bloom shoots attain a much greater 

 length than those of either of the 

 parents. The side shoots make a growth 

 of several feet before any buds are 

 developed . Figure 1 5 shows the enormous 

 growth of this hybrid. It continued to 

 grow for nearly five months after this 

 photograph was taken, finally being 

 killed by a bacterial rot of the root and 

 stem. At the time of its death the hybrid 

 had grown out through the ventilator 

 and for a short way down the roof of 

 the greenhouse on both sides. 



FLOWERS. 



The pediceled flowers of this hybrid 

 are borne on a greatly elongated rachis, 

 which in some cases attains the length 

 of three feet. The flowers of the parents 

 are borne in the same way, though the 

 flowering axis or rachis does not grow to 

 such a length as with the cross. Per- 

 haps the greater length of the rachis 

 was due to the fact that no pods set 

 and therefore all the food went to the 

 development of the flowers. 



The buds of the radish are obovate 

 in shape, while those of the cabbage are 

 oblong-elliptical and much larger and 

 longer. The buds of the cross are a 

 mean between those of the two parents 

 in shape and size. Near the top of the 

 bud of the radish, there are several 

 prominent hairs growing out from the 

 sepals. The cabbage and the radish- 

 cabbage cross do not have these hairs. 



The cross has four petals, intermediate 

 in size between the two parents. The 

 radish parent was dominant in regard 

 to color of the petals, the background 

 color being white with a purjjlish tinge 

 and veins. There was no sign of the 

 rich yellow color of the petals of the 

 cabbage i^arent. 



The radish and cabbage flowers each 

 have six stamens. Most of the flowers 

 of the cross had six stamens but a good 

 many had two extra well developed 

 stamens, making eight. There were 

 about 15% of the flowers which showed 

 this variation. These two extra stamens 



bring up some interesting questions 

 which will be discussed in another 

 article. 



It was noticed that the pollen from 

 this cross was not powdery and light 

 as that of the radish and cabbage, iDut 

 stuck together and had a tendency to 

 ball up. There was often difficulty in 

 spread ng the pollen out on the stigma. 

 On examination it was found that the 

 pollen from the radish and that from the 

 cabbage were very regular in size and 

 shape, while that of the hybrid was very 

 irregular in both respects. Attempts 

 to germinate the pollen from the 

 hybrid in various solutions all failed. 



Most of the ovaries of the hybrid 

 appear to be two-celled like those of 

 the cabbage parent. One slide of a 

 hybrid pistil showed sections of an 

 ovary with three cells. 



STERILITY OF THE HYBRID. 



About crosses between species De 

 Vries says: "Whenever their systematic 

 differences are too great, the crosses 

 will be infertile, even with the pollen 

 of their parents. Repeated crosses are 

 impossible and no practical results 

 can be obtained." Generic crosses are 

 nearly always sterile. Most of them do 

 not even produce flowers and if they 

 do, the flowers are usually aborted in 

 some way. 



In March, 1911, this hybrid started 

 blooming in great profusion. Nearly 

 every day during March, April and May, 

 pollen from different varieties of radish 

 and cabbage, including the parents, 

 and from cauliflower, collards, Brussels 

 sprouts and their crosses, was tried on 

 the flowers of the radish-cabbage hybrid, 

 but nothing resulted. The hybrid was 

 also sterile to its own pollen. Flowers 

 of the radish, cabbage and various 

 Brassica crosses were emasculated, 

 bagged and pollinated with the hybrid 

 I)ollen, without results. The same 

 process of ])ollination was gone through 

 in the winter of 1912 with a root cutting 

 of the hybrid and again resulted in 

 failure. 



