108 



PKACTICAL BOTANY 



It is often a matter of much practical importance to recognize 

 the partially or completely dioecious character of cultivated 

 plants, or, at any rate, the fact that many or all of the individ- 

 uals of a species or variety produce no good pollen. This is well 

 known to be true of strawberries, and so staminate varieties 

 must be planted among those which produce little or no pollen. 

 97. Symmetry of the flower. The calyx and corolla of most 

 flowers of the higher seed plants show some kind of symmetry 



or orderly arrangement 

 of the parts ; that is, the 

 divisions of the calyx 

 or corolla either radiate 



FIG. 96. Begonia flowers, monoacious 

 A : a, staminate flower ; 6, pistillate flower. , twisted stigmas, enlarged 



from a central axis, like the spokes of a wheel from the hub 

 (Fig. 97, .#), or they are arranged with corresponding halves on 

 either side of a central axis (Fig. 98, -5). Flowers on the former 

 plan are said to have radial symmetry or to be actinomorphic (ray- 

 shaped), and those on the latter plan are said to have bilateral 

 symmetry or to be zygomorphic (yoke-shaped). It is considered 

 that the zygomorphic type of flower is in a general way more 

 specialized and of a higher type than the actinomorphic one. 1 

 98. The receptacle. 2 The parts of the flower are borne by the 

 more or less enlarged extremity of the flower stalk, which is 



1 For illustrations consult any good modern flora, e.g. Gray's Manual of 

 Botany, seventh edition. 



2 To THE TEACHER. Unless the class is to do a good deal of work in deter- 

 mination of species of seed plants by means of a flora, most of Sects. 98-105 

 should be omitted. 



