638 PHYSIOLOGY. 



of movement in virtue of which they curve downwards and outwards, 

 so as to come into contact with the fertile stamens, whose anthers open 

 outwardly. In this manner the staminodes become dusted with pollen, 

 and then become uncoiled, assume an erect position, so as to come into 

 contact with the stigma, whose curling lobes twist round them and receive 

 the pollen from them. 



Hildebrand gives the following arrangement of the distribution of 

 sexual relations in flowering plants : 



A. Male and female organs in different flowers (diclinous) ; self-fertiliza- 



tion consequently impossible, and foreign impregnation, accomplished 

 by insect agency or wind, indispensable. Under this head are in- 

 cluded the flowers of dioecious and monoecious plants. 



B. Male and female organs in the same flower (monoclinous). 



1. One sex developed before the other (dichogamoiis). Those flowers 



in which the male organs reach maturity before the female ones are 

 called protandrous, and those in which the female reach maturity 

 before the male protogynom ; self -impregnation is thus naturally 

 prevented, and fertilization is accomplished by insect agency. 



2. Both sexes ^developed at the same time. 

 a. Flowers opening. 



i. Anthers remote from the stigma. 



A. Length of style on different individuals of the same species 



diverse (Heterostylia}. Self -impregnation is not prevented; 

 but, in comparison with impregnation through insect agency, 

 it is either entirely useless for seed-formation, as in Pul- 

 monaria officinalis, or effected only with unimportant results, 

 as in Primula sinensis. 



B. Length of style on different individuals of the same species 



equal. 



o. Sexual organs changing their reciprocal position during the 

 development of the flower. Self -impregnation avoided; 

 impregnation by means of insects facilitated. 

 oo. Sexual organs remaining unaltered in position during the 



development of the flower. 



t Insect agency necessary to fertilization ; self -impregnation 

 in fact impossible, foreign aid indispensable, as in Or- 

 chideae; or self-impregnation possible, but not indis- 

 pensable, foreign impregnation more frequent, as in 

 Asclepiadese. 



tt Insect agency not necessary to fertilization. Self-im- 

 pregnation possible, but impregnation also performed 

 by insects. 



(The possibility of self-fertilization is evident 1, where the flowers are 

 erect and the filaments are longer than the styles, as in Vitis, Chenopodium, 

 &c. ; 2, where the flowers are pendent and the filaments are shorter than 

 the styles, as in Fritillaria imperialis, Convallaria majalis, &c. ; but as all 

 these flowers are visited by insects, cross-impregnation probably often 

 takes place.) 



