9 8 
FLORAL MECHANLSM, ETC, 
occur, but as it will not usually occur before the cross- 
pollination it is likely that prepotency of the latter is the 
rule. Such flowers are Lamium and many other Labiatae 
and allied orders, many Cruciferae, Ranunculaceae, &c., and 
many of the ‘ loose-pollen ’ flowers mentioned below. Every 
gradation is found from those in which cross-pollination is 
the rule to those in which it rarely occurs. 
The loose-pollen mechanism is found in the Rhinanthus 
group of Scrophulariaceae (Euphrasia, Bartsia, &c.), Acan- 
thus, &c. The pollen is dry and pow r dery as in wind-pol- 
linated forms. It is held loosely in a box formed by the 
stamens under the upper lip of the flower, so arranged that 
the entering insect shall open the box and receive a shower 
of pollen. Some of these forms are dichogamous (protan- 
drous), others merely have the stigma projecting beyond 
the stamens. Transition forms occur in Euphrasia, &c. 
A second type of this mechanism, usually with porous 
opening of the anthers, is found in the hanging flowers of 
Borago, Solanum sp., Erica, Calluna, Cyclamen, Soldanella, 
Galanthus, &c. 
In the trap-floivers the visitors are entrapped and are 
either suffered to depart at once by another road past the 
essential organs, or are captured in the female stage of the 
dichogamy and held until the pollen is shed. To the first 
class belong Cypripedium, Coryanthes, Stanhopea, and other 
orchids, &c., to the second Arum and other Araceae, 
Aristolochia 1 , Ceropegia, Aspidistra, Magnolia and others. 
So far we have dealt w r ith mechanisms in regard to the 
favouring of cross-pollination. Arrangements for autogamy 
are equally common, even in most of the highest types of 
flowers. Thus in Compositae the final curling up of the 
stigmas, in a very great number of flowers the withering of 
the corolla, in others merely the movements of insects in 
visiting, bring pollen and stigma into contact with one an- 
other. Details will be found in Part II. 
The most interesting mechanism of this class is the pro- 
duction of a second type of flower which does not open and 
in which therefore only self-pollination can occur. Such 
cleistogamic flowers are well seen in Viola (q.v.), Oxalis, 
1 Note that here a tube occurs in the flower, without any apparent 
reference to insects’ tongues. 
