276 THE THEORY OF THE GENE 



difference in the reciprocal effects, the results do not 

 convincingly demonstrate the probability of the latter 

 interpretation. 



Sex Reversal in Hemp. 



Many of the flowering plants develop both pistils con- 

 taining egg-cells and stamens containing pollen in the 

 same flower, sometimes in different flowers on the same 

 plant. It is not uncommon for the pollen to ripen before 

 the ovules, or, in other cases, the ovules before the pollen. 

 In other plants, the ovules may develop only on one plant, 

 and the pollen on another plant, i.e., the sexes are sepa- 

 rate, the species dioecious. In some of these dioecious 

 plants, however, the organs of the opposite sex may occur 

 as rudiments; occasionally they become functional. Cor- 

 rens has studied a few cases of this kind, and has at- 

 tempted to test the character of the germ-cells of such 

 exceptional cases. 



More recently experiments with dioecious hemp (Can- 

 nabis sativa) by Pritchard, Schaffner, and McPhee have 

 shown that environmental conditions may change a pistil- 

 producing plant (or female) into one in which stamens 

 and even functional pollen are also produced, and, con- 

 versely, may change a staminate plant into one producing 

 pistils containing functional eggs. 



When hemp seeds are planted at the normal time in 

 early spring they produce male (staminate) and female 

 (carpellate) individuals in about equal numbers (Fig. 

 149), but Schaffner has found that when planted in rich 

 soil accompanied by a changed light period, the plants 

 show "sex reversal" in both directions. "The amount of 

 reversal is approximately inversely proportional to the 

 length of daylight." That the same environment should 

 change carpellate into staminate, and staminate into car- 

 pellate plants is at first sight rather surprising, for 



