ANGIOSPERMS. 



425 



already said, can be symmetrically divided by two planes in different ways ; the 

 anterior and posterior halves which are symmetrically alike are different from the 

 right and left halves which are also symmetrically alike ; and the general form of the 

 mature flower corresponds to this arrangement of the parts in Dicentra ; in Fumaria 

 and Corydalis on the other hand the right side is developed differently from the left ; 

 the one produces a spur, the other does not, while the anterior and posterior sides are 

 symmetrical ; in this case therefore the plane of symmetry coincides with the transverse 

 or lateral plane section. In the zygmorphous flowers of some Solanaceae the plane of 



FlG 352. Zygomorphous flower Q{ Columned Schiedeana, one of the Gesneraceae. A an entire flower with two sepals 

 removed. B the androecium. C the gynaeceum. D the coherent anthers enlarged and seen from behind. E transverse 

 section of the ovary. F the diagram. The letters a denote the anthers, en the connectives, f the filaments, n the 

 stigma, g the style, fk the ovary, d the staminode developed as a nectary, // the laterally oblique placentas. 



symmetry and the median plane intersect one another at an acute angle 1 ; but the 

 large majority of zygomorphous, monosymmetrical flowers are so constructed, that the 

 median plane is at the same time a longitudinal section which divides them symmetri- 

 cally, as for instance in the Labiatae, Papilionaceae, Orchideae, Scitamineae, 

 Delphinium, Aconitum, the Lobeliaceae and Compositae, etc. 2 The zygomorphous 

 development is found especially in the lateral flowers of spikes, racemes and panicles, 



1 Such flowers are said to be obliquely zygomorphous ; the expressions median zygomorphous and 

 transverse zygomorphous require no explanation. 



2 In observations of this kind it is necessary to attend to torsions, such as occur in the ovary of 

 the Orchideae, on the flower-stalk of the Fumariaceae, etc. 



