168 HORTICULTURE FOR SCHOOLS 



in Fig. 105. This cell consists of a ground glass ring fastened 

 on a microscopic glass slide with paraffine or vaseline. 1 A 

 glass cover-slip is placed on the top of the ring and held in 

 place by a little vaseline. A few drops of water are put in 

 the bottom of the cell to keep the chamber moist. The pollen 

 is mounted as follows: A drop of the germination medium 

 (sugar solution in this case) is applied to the cover-slip with 

 a glass rod. Pollen is dusted upon the surface of the drop, 

 and the cover-slip is then placed on the vaselined ring so that 

 the drop hangs downward, and is within the moist chamber. 

 The pollen can then be examined with a microscope at any 

 time. (See Fig. 105). 



After the grains are mounted, they begin to absorb moisture 

 through their coats and swell. Soon the viable grains put 

 forth tubes, which continue to grow until they attain con- 

 siderable length. The grains of pollen, on absorbing mois- 

 ture, first change their shape from elliptical to round. Next 

 three protuberances appear. From one of the protuberances 

 the pollen-tube starts, and continues to grow for some time 

 as is shown in Figs. 106 and 107. Many kinds of pollen do 

 not assume this triangular shape before putting forth pollen- 

 tubes. Frequently pollen-grains have certain spots or modi- 

 fied places in their coats for the emission of pollen-tubes. By 

 counting the germinated and non-germinated grains the per- 

 centage of germination can be obtained. An examination of 

 the photomicrographs will show that a high percentage of 

 germination may be expected from almond pollen (Fig. 107). 

 The percentage of germination of pollen of most apple varie- 

 ties is also high. On the other hand, Japanese plum pollen 

 and many varieties of sweet cherry pollen give compar- 

 atively low tests. The hazelnut pollen, Fig. 103, shows a very 



1 While glass rings, which may be obtained from dealers in optical supplies, 

 are best for this purpose, fibre rings or rings of sealing wax may be employed 

 instead. If sealing wax is used, it is softened in a flame and applied to the 

 slide in the form of a circle, after which the top is leveled off with a sharp 

 knife. Hollow ground-glass slides may also be used. 





