452 VEGETABLE PHYSIOLOGY 
may be found in the Gentianacew, Onagracee, Campanu- 
lacew, Composite, &c. In Parnassia the receptive surface 
of the stigma is not even formed until the anthers have 
discharged 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 anemophilous 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 observed in many cases 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 ; diwcious, where they are on different plants ; 
or polygamous, 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 ‘moncecious’ 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 
