442 VEGETABLE PHYSIOLOGY 
their pollen. The second condition is known as protogyny, 
and is the converse of the first, the stigma withering before 
the pollen is mature. This condition occurs in both anemo- 
philous and entomophilous flowers ; certain of the Plantains 
(Plantago) and some grasses (Anthoxanthum, &c.) show it 
in the former group, as does Scrophularia among the latter. 
Something corresponding to dichogamy is found among 
the Ferns, where the antheridia and archegonia on a pro- 
thallium do not mature simultaneously. Cross-fertilisation 
must consequently be the only form possible. The same 
peculiarity may be observed among the Mosses. 
Another means often observed to secure cross-pollination 
is diclinism, or the production of the stamens and carpels 
in different flowers. Diclinous plants may be monecious, 
where the staminate and pistillate flowers are on the same 
plant; diwczous, where they are on different plants; or poly- 
gamous, where a plant bears flowers with stamens and 
carpels as well as others which contain only one or the 
other kind of sporophyll. 
The terms ‘monecious’ and ‘ dicecious’ are sometimes 
applied to the Cryptogams, when their sexual organs are 
upon the same or upon different plants. They then refer, 
of course, to the gametophytic and not to the sporophytic 
phase of the life cycle as in the cases just quoted. 
Some flowers exhibit a peculiarity of form, which is 
an adaptation favouring cross-pollination. The plants 
possess flowers of two kinds, which are specially related 
to each other. The most familiar instance in our own 
flora is the common Primrose, which has five stamens and 
a club-shaped stigma. In some flowers the stigma is 
placed just in the throat of the corolla, and the stamens 
some little way down its tube. In the rest of the flowers 
the positions are reversed. We have here an adaptation 
to the visiting insect, for when it touches the stamens of a 
short-styled form, it covers with pollen the part of its body 
which will come into contact with the stigma of the next 
long-styled flower it alights upon. Another portion of its 
