128 
PLANT STUDIES 
stigma of the same flower are not mature at the same time. 
It is evident that this is a very effective method of prevent- 
ing self-pollination. When the pollen is being shed the 
stigma is not ready to receive, or when the stigma is ready 
to receive the pollen is not ready to be shed. In some 
cases the pollen is ready first, in other cases the stigma, 
the former condition being called protandry, the latter 
protogyny. This is a very common method of preventing 
self-pollination, and is com- 
monly not associated with 
irregularity. 
The ordinary figwort may 
be taken as an example of 
protogyny. When the flowers 
first open, the style, bearing 
the stigma at its tip, is found 
protruding from the urn-like 
flower, while the four 
stamens are curved down 
into the tube, and not ready 
to shed their pollen. At 
some later time the style 
bearing the stigma wilts, 
and the stamens straighten 
up and protrude from the tube. In this way, first the 
receptive stigma, and afterwards the shedding pollen-sacs, 
occupy the same position. 
Protandry is even more common, and many illustrations 
can be obtained. For example, the showy flowers of the 
common fireweed, or great willow herb, when first opened 
display their eight shedding stamens prominently, the style 
being sharply curved downward and backward, carrying 
the four stigma lobes well out of the way. Later, the 
stamens bend away, and the style straightens up and ex- 
poses its stigma lobes, now receptive (see Fig. 134). 
(3) Difference in pollen. In these cases there are at 
FIG. 134. Flowers of fireweed (Epi- 
lobium), showing protandry. In 1 the 
stamens are thrust forward, and the 
style is sharply turned downward and 
backward. In 2 the style is thrust 
forward, with its stigmatic branches 
spread. An insect in passing from 1 
to 2 will almo'st certainly transfer pol- 
len from the stamens of 1 to the stig- 
mas of 2. After GRAY. 
