46 



on the same individual, the plant and flowers are said to be 

 polygamous. A flower which produces no seed is said to be 

 sterile ; this may be because it possesses no pistil, or because its 

 pistils fail to produce seed. 



Symmetry of 42. A flower is normally borne 



in the axil of a bract which is said to subtend the flower, 

 just as an ordinary foliage leaf subtends its axillary branch. 

 That part of the flower which faces the flowering shoot from 

 which it springs laterally is called the upper, superior, or 

 posterior, while the opposite part facing the subtending bract is 

 the lower, inferior, or anterior. The plane which passes through 

 the posterior and anterior part of the flower, and therefore 

 through the parent flowering axis and the middle of the 

 subtending bract, is the median plane, or section, of the flower,, 

 while a vertical plane passing through the flower at right 

 angles to the median plane is called the lateral plane or section, 

 and any other plane which passes through the intersection of 

 these may be called the oblique plane or section. 



A radial longitudinal section of a flower is one which is 

 parallel to its longitudinal axis and passes through the centre 

 of the flower, while a transverse section is one at right angles to 

 its longitudinal axis. 



If in a flower the members of each whorl of floral organs are 

 all alike in size and shape, the flower is regular. If not it is 

 irregular. The regularity or otherwise of a flower is naturally 

 most noticeable in the perianth leaves and especially in the 

 corolla, these being as a rule the most conspicuous part of the 

 flower, and hence when in descriptive botany a flower is 

 spoken of as regular, or irregular, these terms may as a rule be 

 taken to refer to the corolla, or perianth leaves. 



A flower which is divisible in two or more radial longitudinal 

 planes into similar halves, so that in each section one half is to 

 the other as an object is to its image seen in a mirror and the 

 halves in one section are similar to those in the other sections, 

 the flower is actinomorphic. When there is only one radial longi- 

 tudinal section in which a flower can be divided into similar 

 halves it is said to be zygomorphic, and if there is no plane in 

 which it can be divided in this way it is asymmetric. 



The prts of 43. The flower is really a short- 



ate LeavJ enec ^ shoot and its parts, which compose the calyx, 

 corolla, androecium and gynoecium are really nothing 

 but leaves. The flower bud like the bud of an ordinary leafy 

 shoot is either terminal, or it arises in the axil of a leaf, the 

 latter being a normal green leaf, or one which has only been 



