86 proceedings: botanical society 



produced viable seed, the plants from which were accidentally lost. 

 In hybrids between tobacco varieties first generation uniformity and 

 vigor are noticed in a marked degree. 



In the case of oat hybrids Mr. Norton noted that the segregation in 

 the second and later generations was normally Mendelian, though in 

 one or two cases intermediate forms became fixed. There is a distinct 

 coherence of characters shown when naked oats are crossed with the 

 ordinary hulled type. Naked oats have more than three grains to the 

 spikelet, while in hulled oats the spikelets are limited to two or three. 

 The first generation gives a peculiar intermediate, while in the second 

 the parent types reappear with the intermediates in a 1:2:1 ratio, 

 showing complete coherence of the two pairs of characters. While 

 this coherence has not been split, two strains of the intermediate type 

 were fixed. 



Of asparagus hybrids a peculiar case was mentioned. Asparagus 

 davuricus, a Chinese species, when crossed with pollen of Asparagus 

 officinalis gave a progeny that resembled in most characters the A. 

 davuricus mother, with the exception of a greater vigor. The first 

 generation plants dropped their branches in the fall like A. davuricus. 

 These hybrids were crossed back with A. officinalis, but the second gen- 

 eration showed none of the abcission phenomena exhibited by their 

 mother parent, although the expected ratio was 1:1. One of the first 

 generation plants of this cross shows a vine-like habit, a character not 

 present in either parent or in any close relative, although vining is 

 common in other sections of the genus. 



Dr. W. A. Orton discussed the behavior of disease resistance in 

 hybrids, with special reference to the wilt diseases of cotton, okra, 

 watermelons, and cowpeas, caused by the well-known vascular parasite 

 belonging to the genus Fusarium. 



In cotton, resistance which occurs in rare individuals is separated 

 out by selection, and the crosses discussed were made between such 

 resistant strains and other varieties of Upland cotton. 



Certain conditions impair the exactness of results with reference to 

 Mendelian ratios. The strains used were not of pure type and the 

 most resistant show some disease; uniform exposure to infection is se- 

 cured with difficulty; the severity of the disease varies with weather 

 conditions. Susceptible plants are killed and their progeny are not 

 available for further study. 



In the first generation in cotton hybrids wilt-resistance is dominant, 

 only a small percentage showing disease, usually less than that of the 

 resistant parent. In the second generation there is a segregation of the 

 wilt-resistant character and a large percentage of non-resistant plants 

 are produced. In reciprocal crosses an effect from the female parent 

 is apparent in the second generation. By selection from the resistant 

 plants the selected third generation shows a marked increase in 

 resistance. 



In the cowpea wilt-resistance seems to be limited to a distinct variety, 

 the Iron. In the first generation of crosses with other varieties wilt- 



