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 



FIG 352. Zygomorphous flower olColitmnea Schiedeana, one of the Gesneraceae. A an entire flower with two sepals 

 removed. B the androeciuni. 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, y^the filaments, 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 Fumnriaceae, etc. 



