Varietäten, Descendenz, Hybriden. 629 



pods of ihe first-generation hybrids of the Velvet with the Lyon, 

 Yokohama, and China, are closely covered with more or less 

 appressed stinging bristles, mostly grayish yellow, but usually with 

 a patch of red at the base of the pod. The bristles from the three 

 hybrids could not be distinguished, even with the microscope. 

 These bristles are shorter and thinner than those of the wildgrowing 

 S. pruritum and have less gum in the tip. They also sting less. 



The Chief types of plant-hair appearing in the second-gene- 

 raton are: 



1. stinging bristles, aboiit one and a half millimeters, or more 

 (stinging); 



2. fine down, about halt a millimeter (downy); 



3. coarse down, up to about threequarters of a millimeter (downy); 



4. intermediate between downy and stinging about one millimeter, 



5. long tomentum over one millimeter long, like that of the 

 Velvet bean, with a patch of black tomentum on the calyx, but 

 white pubescence on the rest of the plant ("Velvet"); 



6. long tomentum, usually softer and blacker than n^. 5, but ac- 

 companied with black tomentum over the whole of the plant (long 

 black); 



7. Short tomentum, less than half a millimeter, accompanied by 

 black tomentum over the whole plant and serious floral abnorma- 

 lities (smooth black). 



In the cross Velvet-Yokohama there were no fine downy 

 pods. The cross Velvet-Lyon so many plants with white pubes- 

 cence set no pods that the proportions are rendered unreliable. 

 From the close agreement of the other two crosses with the calcu- 

 lated raost probable numbers, the author thinks that the proportions 

 are: stinging 9 : downy 3 : "Velvet" 1 : black 3. 



The writer's working hypothesis, derived from his cultures of 

 Fg, F3, F4 and F^^, is: 



Tf B is a positive genetic difference (or factor) which the Velvet 

 bean lacks, but which is present in the Lyon, Yokohama and 

 China; and C is anolher factor, present in the Velvet bean, but 

 absent in the other tree; and both B and C (either Single or double) 

 are needed for the production of typical stinging bristles; then in 

 the second generation: 



1. The stinging plants have both the factors B and C, Single 

 or double: 



2. The down}'' plants have only the factor B, Single or double; 



3. The long black and "Velvet" plants have only the factor C, 

 Single or double; 



4. The smooth black plants have neither B nor C. 



If D is a genetic factor, present in the Lyon and Yokohama, 

 but absent in the Velvet bean, which factor, in the absence of B, 

 causes the formation of black tomentum all over the plant; if be- 

 tween factors C and D there is a partial repulsion, so that they 

 rarely enter the same gamete; then: 



1. Plants with neither C nor D will be very rare in F.2; 



2. Plants with both C and D will be about twice as numerous 

 in F2 as plants with only C; most of the former will have Single, 

 and most of the latter double factors; 



3. Plants with D only will mostly have this factor double, and 

 will be about half as numerous, as plants with both C and D. 



We have then for the segregation in Fj: 



1. Nine-sixteenths, stinging plants, all with B and C, about 



