STUDIES IN POLLEN, WITH SPECI’.L REFERENCE TO LONGEVITY 761 
the maturity of the tassel, and the amount of water available to the plant. 
In illustration of this, pollen freshly gathered in the field showed 52 per 
cent of water, while pollen gathered in the laboratory, from tassels standing 
in a jar of water, contained 63 per cent of moisture. Andronescu (1915) 
states that corn pollen has an average moisture content of about 57 per 
eent. As will be shown later, it loses moisture rapidly on exposure to 
conditions of low humidity. 
Method of pollen germination 
In all artificial germinations the following method was used: A small 
quantity of pollen was placed in a drop of sugar solution or sugar-agar 
solution, on a cover glass. The cover_glass was then inverted over a Van 
Tieghem cell which contained several drops of the same solution. Vaseline 
was placed arourd the edges of the cell to secure the cover glass and to 
prevent evaporation 
Germination of Antirrhinum pollen 
Antirrhinum pollen germinated well in a cane-sugar solution, very high 
percentages of germination resulting. There was no very great sensitive- 
ness as to concentration. At one time the highest percentage of germi- 
nation would result at one concentration, at other times, at another. In 
general, the best germination was obtained in a 15- to 25-per-cent cane- 
sugar solution. There was a smail percentage of germination in water. 
The range of concentration at which germination occurred is shown in 
table 2. In other experiments a higher percentage of germination, even 
as high as 80 to 90 per cent, was obtained. 
TABLE 2. GERMINATION OF ANTIRRHINUM POLLEN 
Cane sugar (per cent)........... ny 10 15 20 25 30 
Germination (per cent).......... 38 18 42 70 ay I! 3 
As the germ-tube growth progressed, a thickening of the tube wall 
occurred at several points back of the growing tip. These areas increased 
in thickness until finally the whole tube was plugged with callose. These 
callose plugs can be seen in unstained slides, but a short immersion in 
