HORTICULTURE 149 



stigma. Perhaps a long "spell" of wet weather may even kill the 

 pistils after they have been fertilized. 



Thus a rain during the blooming season may decrease the set- 

 ting of fruit in four ways: (1) By preventing the pollen from 

 reaching the stigma, both because it is too wet to fly and because 

 pollen-carrying insects are absent. This is important only when the 

 rain lasts several days and most of the pistils pass their receptive state 

 before the rain ceases. (2) By destroying the vitality of the pollen. 

 (3) By injuring the stigma. (4) By preventing fertilization or the 

 germination of the pollen because of low temperature. 



The Blossoms May Be Injured by Strong or Drying Winds. 

 Near the sea and large lakes, fruit blossoms may be whipped off by 

 very severe winds. In such cases a mixed windbreak of deciduous 

 and evergreen trees may be used to advantage. Drying winds during 

 the blossoming season are not common in the east but are often 

 serious in some parts of the west. Luther Burbank, one of our best 

 observers and experimenters in orchard pollination, says a dry wind 

 sometimes causes a short fruit crop in some parts of California by 

 drying up the juices of the stigma so that the pollen cannot ger- 

 minate. 



SELF-STERILITY. 



There are some trees which blossom full year after year but 

 set little or no fruit, even in the most favorable seasons. These trees 

 are usually in solid blocks, or at a distance from any other variety. 

 Planting near them other trees of the same variety does not make 

 them fruitful ; but if trees of other varieties are planted near they are 

 often made fruitful. A self-sterile variety is one which is unable to 

 set fruit when alone; in order to be productive, it must be planted 

 near some other variety. Two varieties very commonly self-sterile 

 are Miner and Wild Goose plums. Large blocks of the Kieffer pear 

 and some of the great prune orchards on our Pacific Coast have been 

 unprofitable from this cause. 



In general, the cause of self-sterility is that the pollen of a 

 variety is unable to fertilize the pistils of that same variety. That 

 is, if pollen from a Wild Goose blossom falls on a Wild Goose pistil, 

 whether on the same tree or any other Wild Goose tree, no fruit will 

 result as a rule. The pollen of a self-sterile variety may be and gen- 

 erally is produced in abundance and is well formed. Wild Goose 

 generally bears pollen freely, although it is one of the most self-sterile 

 varieties in cultivation. The Bartlett pear is often self-sterile, yet its 

 pollen is perfect. The pollen of a self-sterile variety also has vitality, 

 for it will fertilize the pistils of other varieties. For example, plant 

 together trees of the two self-sterile varieties, Miner and Wild Goose, 

 and both will often be made fruitful, because the pollen of each, 

 though infertile on itself, is fertile on the other. 



The practical bearing of the self-sterility problem is this : There 

 are certain varieties of fruit which we wish to grow largely for the 

 general market, but we find that they are not productive when 

 planted alone. They need the pollen of other varieties to make them 

 fruitful. Other varieties must be planted near them as pollinizers. 



