84 
IOWA ACADEMY OF SCIENCES. 
an excellent illustration of a plant that is just changing 
from hermaphrodite to bisexual. He places the plums in 
several groups based on the structure of the flower. Those 
groups are as follows, the Dichogamous with some mem- 
bers proterogynous and others proterandrous, the Heter- 
ostyled with the long and the short styled forms, the Bi- 
sexual with flowers either andromonoecious or gynodioe- 
cious, and the Hermaphrodite. In these forms he reads the 
various steps in the future evolution of the flower. It seems 
as though this classification was rather arbitrary, for 
other students of the question have been inclined to 
ascribe these variations to climate, etc., rather than to an 
inherent variability. Waugh (21) finds that some individ- 
uals are markedly proterogynous, the pistil being exposed 
and receptive even before the opening of the blossom, in 
others there is normally a lack of pistils, and still others 
have very long pistils. Even in this classification we are 
ied to wonder just how much is due to a natural tendency 
to vary, or to abnormal changes brought about by environ- 
ment; and whether these could be rightly classed as nat- 
ural adaptations to cross pollination. 
The length of the blossoming season depends very largely 
on the weather. If conditions are favorable the flowers 
are all pollinated within a day or two, and the petals fall 
two or three days later. If pollination does not occur the 
flower remains for several days longer. 
The pollen tube is formed very soon after the application 
of the pollen to the stigma. It gradually descends through 
the tissue of the style until it reaches the ovule. The pro- 
cess of fertilization occurs in from one to two weeks. One 
of the figures illustrates the pollen grain as it germinates 
in a three per cent dextrose solution. The pollen germinates 
very readily under these conditions. The question of the 
relation of the temperature to the germination has been 
discussed by Goff (9) who finds that some varieties will 
germinate even in cold vceather at a temperature of 51° F., 
and would even show some slight power of germination 
after being exposed to a freezing temperature. From these 
facts and the fact that the pollen will germinate after the 
