126 FLORAL DIAGRAM [CH. 



no plane in which it can be cut into two symmetrical 

 halves. 



These examples will suffice to show that the terms 

 regular and irregular refer merely to the similarit}^ or 

 otherwise between the parts of each w^horl, whereas the 

 more modern terms actinomorphic, zygomorphic, and 

 asymmetric refer to the planes of symmetry of the 

 flower. 



On looking down into a flower it is usually possible 

 to directly observe the plan of arrangement of the parts, 

 and it is often convenient to adopt a consistent system of 

 signs and diagrams to represent this. 



If we project the spiral line joining the insertions of 

 the successive organs in the terminal flower of a Barberry 

 (Fig. 17), for instance, and mark on it at the relatively 

 proper distances the organs themselves which may be 

 conveniently done by diagrammatic sections of each sepal, 

 petal, stamen, and carpel a conventional figure known 

 as a floral diagram is obtained, such as those shown in 

 the accompanying illustrations. 



Obviously the empirical diagram, representing merely 

 the projection into one plane of what is actually visible 

 in an open flower, may be added to by indicating organs, 

 relations in space, displacements, &c., not directly observ- 

 able in the field but inferred from comparisons with other 

 flowers and from the study of development, &c., and so 

 converted into a theoretical diagram. 



For instance the floral diagram of a Veronica (Fig. 

 30, C) shows only two stamens, but that of most Scrophu- 

 lariacesB has four (Fig. 30, B), and since some have five 

 (Fig. 30, A), and several exhibit a rudimentary out- 

 growth in the position of the fifth stamen, there is evi- 

 dence for regarding the theoretical diagram of Veronica 

 as retaining tAvo perfect stamens and as having lost three. 



