430 Plant-Breeding 



and each student draws blindly from the bag one seed at a time, 

 recording his draw. This exercise illustrates segregation and 

 the formation of gametic cells. 



4. Now each student may remove simultaneously one pea 

 from each of two bags, and lay them down side by side to illus- 

 trate the mating of gametes in an FI hybrid and the subsequent 

 recombination of characters. He should record only the domi- 

 nant characters present in each pair taken and his record will 

 show the phenotypes of his F 2 hybrids. 



5. The same principles can be illustrated by the use of a pack 

 of playing cards. Draw at random two cards at a time. Record 

 each combination observed. Two blacks coming simultaneously 

 represent a homozygous black individual; a black and a red 

 represent a heterozygous form appearing as black, two reds 

 represent a pure recessive. For illustrating the combination of 

 two character pairs, four cards may be drawn at a time. 



6. Some simple chemical reactions 1 afford an excellent series of 

 demonstrations illustrating the main features of Mendelism. 

 The following apparatus and chemicals are required : 



4 500 cc. flasks 3 dozen test tubes 



1 100 cc. flask 4 small funnels for burettes 



1 100 cc. graduate 1 iron stand and clamps 



4 50 cc. burettes 3 test tube racks 



1 2 cc. pipette 1 pipette dropper 



500 cc. 10% cp. NH A OH 500 cc. 5% cp. HCl 



500 cc. 25 % cp. NHtOH 100 cc. 2 % litmus powder 



500 cc. 10% cp. HCl solution 



10 cc. phenolphthalein 



While the burettes are not absolutely necessary, they will 

 greatly facilitate the demonstrations. The solutions are to be 

 made up beforehand by the instructor, who should try some pre- 



1 This portion of the exercise is based on an article by G. H. Shull, 

 "A Simple Chemical Device for illustrating Mendelian Inheritance," 

 Plant World, 12: 145-153, 1909. 



