THE SIMPLEST RATIO IN A DIHYBRID CROSS 



Living diagram showing the result of crossing a heterozj'gous purple armed Jimson Weed (Hybrid 

 PAr) with a double recessive (Win). Each of the four possible classes of progeny (described 

 under the preceding figure) is equally represented, giving a 1:1:1:1 ratio. (Fig. 14.) 



has been grown to a height of over 6 

 feet. It is self -fertile and selfed seed 

 may be obtained by merely bagging the 

 unopened flowers. A bud may be cas- 

 trated just before the stamens open and 

 the stigma pollinated at once from 

 another unopened bud. Thus the time 

 consumed in making crosses is reduced 

 to a minimum. A single cross-pol- 

 linated flower, moreover, may produce 

 upwards of 600 seeds. The productiv- 

 ity is enormous. A single vigorous 

 plant may have a diameter of over 6 

 feet and has been estimated to produce 

 around 50,000 seeds. Students have 

 figured out that if all seeds were sown 

 and grew to plants of the same size and 



productiveness, it would take only five 

 generations at this rate, including the 

 first plant, to cover the entire surface of 

 the earth, both land and water, and 

 there would be left over sufficient seed 

 to sow several of the planets in addition. 

 As found growing wild, Jimson Weeds 

 occur in two color forms. Those with 

 green stems and white flowers have 

 been called Datura Stramonium, while 

 those with purple stem and purple flow- 

 ers are called Z). Tattila. They hybridize 

 readily, however. The color of the stems 

 shows as soon as the plants break 

 ground in the seed pan. The purple 

 color is dominant; selfed seed from 

 plants heterozygous for stem color 



129 



