BOTANICAL EVOLUTION. 465 
termed dichogamy, is very common; in some plants protandry, or the 
maturing of the stamens first, is the rule: while in others protogyny, 
or the maturing of the stigma, first prevails. Thus in most 
composites (daisy, &c.), and their allies, protandry is nearly universal. 
We may see this well ina Zodelia. The stamens of the former have 
their anthers joined into a tube, and by the time they are mature the 
style forms a club-shaped head, the apex of which just closes up the 
bottom of the tube. Into this tube the anthers discharge all their 
pollen, filling it up. Meanwhile the style elongates, and comes up 
through the tube, like a ramrod through a gun-barrel, carrying all 
the pollen before it. At this stage any bee or other insect visiting 
the fiower for nectar will get its body dusted over with pollen. The 
style, however, still continues to elongate until it reaches its full 
length, when the stigmatic faces which have hitherto been in close 
contact, open out widely. Any pollen left adhering on the style will 
be on the outside of the style branches and not on the stigmatic 
surfaces, so that it is impossible for this flower to be self-fertilized. 
But if at this stage, a bee which has been visiting flowers at the first 
stage and is consequently carrying pollen on its body, visits this 
flower, some of the pollen will adhere to the stigmatic surfaces and 
thus fertilization will ensue. There are thousands of species of 
plants which are in this way quite incapable of self-fertilization ; they 
are male flowers in the first stage and female flowers in the second. 
If you examine a Tutu plant (Coriaria ruscifolia) just now (Septem- 
ber) you will see a striking example of the opposite mode of arriving 
at a separation of the sexes, viz., protogyny. When the flowers first 
open, five bright red stigmas protrude from them and remain exposed 
for two or three days, so as to catch any grains of pollen which may 
be floating about in the air. In due course they wither, and then ten 
stamens, which, meanwhile have been lying hidden, quickly elongate 
their filaments, and as soon as they are quite mature the anthers 
scatter their pollen to the four winds of heaven. These flowers are 
as incapable of self-fertilization as are those of the Lobelia, but you 
will notice that in both extremes, though any individual flower is so, 
it does not follow that it is not capable of being pollinated by another 
flower on the same plant which opens some days eazlier or later, as 
the case may be. But here sometimes comes in another principle. 
Even among flowers capable of self-fertilization, it has been ascer- 
tained that after this ,has apparently taken place, if pollen from 
another flower be placed on the stigma, this foreign pollen seems to _ 
exercise a more potent influence on the flower than its own pollen can 
do, and if too great an interval of time has not been allowed to clapse 
it will send its tubes into the ovules sooner than that first applied. 
But among most flowers in which complete dichogamy prevails, the 
pistils are as indifferent to pollen brought from other flowers on the 
same plant, as they are to their own. In all such plants every flower 
is at one stage of its existence male only, at another female only. 
Another mode of preventing self-fertilization has been acquired 
by many species of Primula as weil as numerous other plants, and is 
termed Heterostylism.* Thus in the common cowslip two distinct 
forms have been evolved; in one the style is so long that the button- 
*See a recent article by Grant Allen on ‘* Primroses and Cowslips,” in the 
“English Illustrated Magazine” for March, 1885, (p. 303).—-d. 
