GROUP IV. — PHANEROGAMIA: ANGIOSPERMJ;. 



499 



be borne in mind, a general plan of arrangement will be detected, 

 and the individual peculiarities of arrangement, quite apart from 

 any variation in the form of the oi'gans, will be seen to be due 

 either to the suppression of one or more whorls or of one or more 

 members of a whorl, or, more rarely, to a multiplication of the 

 whorls or of their members. If, however, the organs which are 

 absent, but which should typically be present, be indicated in the 

 empirical diagram by dots, it becomes a theoretical diagram. In 

 this way it is possible to arrive at general types on which large 

 numbers of flowers are constructed. Fig. 313, for instance, is 

 the empirical diagram of the flower of the Lily, and it is at the 

 same time the type on which the flower of Grasses (Fig. 314) is 

 constructed in which certain organs are suppressed. 



In constructing a floral diagram the position of the main axis 

 should be indicated by a dot placed above the diagram : the 

 bract, which would of course be exactly opposite to it, may or may 



Fig. 313.— Floral Diagram 

 of a Lily, 



Fig. 314.— Floral Diagram 

 of a Grass. 



Fig. 315.— Floral Dia- 

 gram of a Crucifer ; the 

 median stamens are 

 duplicated. 



not be indicated : the side of the flower toward the main axis is 

 paid to be posterior^ and that toward the subtending bract, anterior. 

 A plane which passes through the flower and also through the 

 main stem and the median line of the bract is termed the median 

 plane or section of the flower : the plane which cuts the median 

 plane at right angles is the lateral plane or section: and the 

 plane which bisects the angles made by the intersection of the 

 median and lateral planes is the diagonal plane or section : any 

 plane other than these is said to be oblique. By means of these 

 conceptions the position of the parts of a flower may be accurately 

 indicated: thus, in describing the flower of the Cruciferse (Fig. 

 315), the two external sepals lie in the median plane; the two 

 inner sepals, the two outer stamens, and the two carpels, in the 



