CHAPTER XXVIII 

 UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 



Practically every phase of the environment to which the plant is 

 subject just before, at and shortly after the time of blossoming has 

 some effect on fruit setting. The influence may make itself felt through 

 rendering the plant or the variety more or less completely dichogamous, 

 through the production of more or less defective pistils, ovules, embryo 

 sacs or pollen grains, through affecting compatibility, indirectly through 

 aiding or interfering with pollen transfer or in a number of other ways. 



Nutrient Supply. — It is often impossible to distinguish clearly between 

 the influence of nutritive conditions within the plant and of conditions 

 of nutrient supply without upon fruit setting, fruitfulness and fertility. 

 Though the nutrient supply available to the plant probably acts upon 

 fruit setting and development largely through first influencing nutritive 

 conditions within, there are so many cases in which the association 

 between the two is so evident that the intervening effect of the environ- 

 ment upon nutritive condition within is overlooked. Furthermore, 

 nutritive conditions within the plant are controlled more readily by 

 affording or withholding certain nutrients than by most other means. 

 It is therefore desirable to give some attention to nutrient supply as it 

 influences fruit setting and fruitfulness. 



. Darwin" states that much manure renders many kinds of plants 

 completely sterile. He cites Gartner as authority for the statement that 

 sterility from overfeeding is very characteristic in certain families, 

 Gramineae, Cruciferse and Leguminosae being mentioned specially. In 

 India Agave vivipara is said invariably to produce bulbs but no seeds when 

 grown in a rich soil, though when it is grown in a poor soil without too 

 much moisture the converse condition holds. ^s On the other hand 

 extreme poverty of soil often leads to dwarfing and sterility, certain spe- 

 cies of clover being mentioned particularly in this connection." Sand- 

 sten^^^ found that excessive feeding of tomatoes caused abnormal flowers. 

 In some instances the stamens almost aborted; in others the pistils were 

 greatly thickened and overgrown. There was a general tendency for the 

 overfed plants to produce fruits with fewer seeds. Two plants produced 

 seedless fruits of normal size. Though these two plants produced many 

 flowers they set fruit poorly. The Jonathan apple, which is usually self 

 sterile or nearly so on rich land in Victoria (Australia) , becomes self 

 fruitful when grown on land of low productivity." The Hope grape, 



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