Photograph from U. S. Department of Agriculture 

 SELF-POLLINATION VERSUS CROSS-POLLINATION 



These two twigs, both shown in natural size, were in equally good situations on the same 

 bush, contained the same number of flowers, all pollinated by hand at the same time with 

 equal care, and the fruits were photographed on the same day. The only difference in treat- 

 ment was that the pollen used on the left-hand twig came from other flowers on the same 

 bush, while the pollen for the right-hand twig was taken from another bush. The cross- 

 pollinated flowers produced a full cluster of handsome berries. The self-pollinated flowers 

 produced no ripe fruit, all the berries that set remaining small and green and later dropping 

 off, until at the time the photograph was taken only two imperfect ones remained. A plan- 

 tation made up wholly from cuttings from a single bush would produce little or no fruit. At 

 least two original propagation stocks are necessary. 



greenhouse there is no accumulation of 

 sugar, the starch remains in storage, and 

 no growth takes place. 



THE BUDS ARE PUSHED OPEN BY ENOR- 

 MOUS INTERNAL PRESSURE 



Along with the formation of the sugar, 

 and caused in part by its accumulation, 

 there develop within the minute cells of 

 the plant enormous internal osmotic pres- 

 sures, which enable the plant to push its 

 buds open. 



These pressures are frequently as high 

 as seven atmospheres, or more than 100 

 pounds to the square inch — a stress that 

 would start a leak in a low-pressure 

 steam-engine. The pressures may be- 

 come as high as 30 atmospheres, or 450 

 pounds to the square inch — a force suffi- 



cient to blow the cylinder head off of a 

 thousand-horsepower Corliss engine. 



The reason that the plant does not ex- 

 plode is because it is broken up into many 

 extremely small and strongly built cells 

 instead of having one big interior cavity. 

 These minute chambers are often as 

 thick-walled proportionally as an artil- 

 lery shell and, in the case of the starch- 

 storage cells of the blueberry, are clearly 

 of such construction as to be able to 

 withstand enormous pressures. 



It turned out that a full understanding 

 of the behavior of blueberry stems when 

 exposed to prolonged chilling was of the 

 utmost importance in the treatment of 

 blueberry cuttings. Limitations of space 

 prohibit the discussion of other phenom- 

 ena encountered in the experiments. It 



544 



