124 



REGULAR AND ACTINOMORPHIC, ETC. 



[CH. 



may be thus cut into similar halves, and in some species 

 of Sempervivum as many as a dozen or more such planes. 



In these cases the flower is 

 more than merely regular- 

 a word which simply signifies 

 that the parts of each whorl 

 are similar to each other in 

 appearance and are regularly 

 arranged round the floral axis 

 for they are also actinomor- 

 phic, i.e. radiate ly arranged so 

 that the flower can be cut into 

 similar halves through more 

 than two planes of symmetry. 

 In contrast to these cases 

 we may examine the irregular 

 flower of a Pea. Here it is 

 clear we can only cut the whole 

 flower into two similar halves by a vertical cut passing 

 through the large posterior petal (standard) and the keel : 

 in any other than this median vertical plane the section 

 results in two dissimilar halves. The flower is monosym- 

 metrical and zygomorphic. The same is true of Linaria 

 and Veronica (Fig. 30, B, C). 



Fig. 29. Floral diagram of 

 Primula acaulis. It is regu- 

 lar and actinomorphic : similar 

 halves are obtained by a verti- 

 cal section passing through the 

 middle line of any sepal (Ei). 



Fig. 30. Floral diagrams of A, Verbascum nigrum\ B, Linaria vul- 

 gar is ; C, Veronica Chamcedrys (Ei). 



