POLLEN AND PISTILS OF APPLES 405 



leaves of Vicia faha. He concluded after germinating the pol- 

 len of a number of plants, that, in general, germination de- 

 pended upon a proper water supply. 



In the germination of the pollen of the second class, in addi- 

 tion to water the addition of some chemical substance has been 

 found to increase the percentage of germination. The addition 

 of various percentages of sugar has been found helpful in ger- 

 minating the pollen of many species. Rittinghaus (18) and 

 Max Pfund (17) found that the pollen of a large number of 

 species would germinate in cane sugar solutions, the concentra- 

 tions ranging from 20 to 50 per cent. Kny (8) and Mangiu 

 (12) found that better germination was secured when gelatin 

 was added to the sugar solution. Careful investigations of the 

 function of those substances such as sugar, gelatin and some 

 others which seem necessary for the germination of the pollen 

 of some species may show that they function only in controlling 

 water absorption. In some cases there is evidence that the pol- 

 len uses the sugar as a food. In some cases, the substance seems 

 to act as a stimulant and only very small percentages are re- 

 quired. Molisch (16) found that the addition of about 0.01 per 

 cent of calcium malate or malic acid to the sugar solution caused 

 the pollen of Azalea and Rhododendron to germinate. In the 

 germination of pollen of some species of Erica and Menziesia, 

 Lidfors (9) observed that the addition of a small amount of citric 

 acid to the sugar solution increased germination. Burck (2) was 

 able to germinate the pollen of some species of Mussaendn, Bego- 

 nia, and Pavetta in distilled water only after the addition of a 

 portion of the stigma or a trace of levulose. Sandsten (19) 

 found that a slightly acid medium is required for the germina- 

 tion of tomato pollen. 



I^oth Strasburger (21) and Tokugawa (22) have shown that 

 in many cases pollen will germinate on the stigmas of plants 

 differing widely in relationship. T'lie pollen of some ^Monocotyle- 

 dons germinated on the stigmas of Diootyled'ons, and vice versa. 

 In ealh case the tubes penetrated the stigma ,but their growth 

 was checked in the style and hence they did not reach the ovules. 



As to the content of pollen, Van Tieghemi (23) found that the 

 pollen of many plants at the time of pollination contains much 

 starch which disappears as germination proceeds. Sandsten (19) 

 found starch in the pollen of a number of plants but does not 

 state the age of the pollen or whether or not apple pollen was 



