82 



THE FLOWERING PLANT. 



Fig. 38.— Floral Diagram of White Lily. 

 st. stem on posterior side of flower ; 

 m.pl. median plane; tr.pl. lateral 

 plane; ob.pl. oblique planes; 1, 1, 

 1. sepals; 2, 2, 2. petals; 3, 3, 3. 

 outer stamens ; 4, 4, 4. inner sta- 

 mens ; 5, 5, 5. carpels : all in alter- 

 nating whorls. 



The relation of parts in a flower to one another and, in a 

 lateral flower, to the main axis is conveniently represented by 

 a floral diagram which may be regarded as a generalized ground- 

 plan (fig. 38). The position of the axis is shown by a dot ; the 

 sepals, petals, and stamens are represented by conventional 

 marks; and the carpels by a rough drawing of their appearance 



in cross-section. A line drawn 

 through the axis dot and the centre 

 of the diagram serves to represent 

 the median or antero-posterior plane, 

 which divides the flower into right 

 and left halves. A line running 

 through the centre of the diagram 

 perpendicular to the. first line there- 

 fore represents the lateral plane, a 

 vertical plane at right angles to the 

 median plane, which divides the 

 flower into a posterior half next 

 the axis and an anterior half turned 

 away from it. Two oblique vertical 

 planes intersecting the preceding at 

 45 degrees may also be represented 

 in the diagram. It may seem unnecessary to distinguish so many 

 imaginary planes, but it is very convenient in practice to designate 

 particular parts of the flower as anterior, posterior, or oblique. 

 In the Pea-flower family, for example, there are five sepals, of 

 which one is always anterior. This is, therefore, one of the 

 distinctive features of the family. 



A study of the innumerable sorts of flower actually existing 

 shows that for cyclic forms the most typical condition consists in 

 the possession of six whorls, all the whorls having the same 

 number of parts, and the parts of successive whorls alternating, 

 just as in decussate foliage leaves. Such a flower, say, with five 

 members per whorl, can be represented either by a floral diagram, 

 or as follows, the dashes representing the floral leaves, which are 

 supposed to be picked off and laid in straight lines : — 



. Sepals. 



. Petals. 



Stamens 

 (outer). 

 Stamens 

 (inner). 

 Carpels 

 (outer). 

 Carpels 



(inner). 



