432 SCIENCE PROGRESS 



Similarly twenty-five of the fifty "dwarf" egg-cells would meet 

 " tails " and twenty-five " dwarfs," or briefly : 



25 DT 

 25 DD 



The total result therefore is : 



25 TT 

 25 TD 

 25 DT 

 25 DD 



Now we already know that the result of the union of a " tall" 

 with a " dwarf" germ-cell is a hybrid which is tall, and Mendel 

 found that it made no difference whether the tall character 

 was carried by the male parent and the dwarf by the female, 

 or vice versa. So that the above result can be written : 



25 TT (Pure Tails) 



50 T D (or D T) (Hybrid Tails) 



25 D D (Pure Dwarfs) 



The result of the random union of two sets of germ-cells, 

 each set consisting of 50 per cent, of germ-cells bearing the 

 Recessive and of 50 per cent, bearing the Dominant character, 

 can be admirably illustrated by drawing one counter at random 

 from a hat containing fifty Red and fifty White counters, and 

 another from another hat with similar contents, and by placing 

 the three kinds of pairs in three separate rows on the table, 

 according as whether they are R W, R R, or W W. The larger 

 the number of trials you make the closer will the approxi- 

 mation to the proportion of 25 R R, 50 R W, 25 WW be. 

 Counters are worse than marbles for illustrating this, by 

 reason of the difficulty of thoroughly shuffling them. But 

 they are better than them, because the phenomenon of domi- 

 nance and the proportion 3 : 1 can be illustrated with them, 

 the former by merely making it a rule to put the red counter 

 on the top of the white when a red and a white are drawn 

 together, the latter by superposing the upper counter in every 

 pair so carefully that the lower one is invisible. If this is done 

 effectively there will be seen, at any rate from a slight distance, 

 to be 75 per cent, red counters and 25 per cent, white. But 

 if you jog the table the difference between the previously 

 apparently identical reds will be revealed. It is also very 



