XXI. 



SEX IN FRUITS.' 



Since the demonstration of the value of sprays for 

 exterminating the insect and fungous enemies of fruits, 

 the most important advance in American pomology is 

 the discovery that some varieties of fruit are unable to 

 fertilize themselves. Much of the failure of apples and 

 pears and native plums to set fruit, even when bloom is 

 abundant, is unquestionably due to too continuous or 

 extensive planting of individual varieties ; and it is safe 

 to expect that other fruits are also jeopardized by un- 

 mixed planting. This knowledge, as soon as it becomes 

 more extensive and exact, is sure to modify greatly the 

 planting of orchards. But there is also an important 

 philosophical side to the problem which I wish to sug- 

 gest at this time. Why are varieties infertile with 

 themselves ? What relation does such infertility bear 

 to the evolution of varieties ? Is it likely to increase 

 or diminish in future varieties ? 



When sex first appeared, the individual was her- 

 maphrodite ; that is, the two sexes were present in the 

 same organism. The two sexes are opposed to each 

 other in their physiological evolution, however, the 

 female sex -elements probably being developed from the 

 constructive or vegetative (anabolic) changes within the 



I Read before the Michigan Horticultural Society, June 14, 1893. Printed in 

 Rept. Mich. Hort. Sop. 1893, 207. For a discussion of the untechnical terminology 

 of sex, see the foot-note, page 66. 



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