194 PRACTICAL BOTANY 



DEVELOPMENT OF THE FLOWER. 



In order to trace the development of the flower it is 

 found convenient to use plants with aggregated 

 inflorescences, i.e. those in which the flowers are 

 closely associated together in large numbers. By cutting 

 sections through such an inflorescence many individual 

 flowers, illustrating different degrees of progress, will be 

 traversed, and by comparison of these an idea of the 

 course of development may be gained even from a 

 single section. 



I. Examine young capitula of the Sunflower with 

 the naked eye : they occur in the same positions as the 

 vegetative apical buds, but differ externally from these 



1. In their greater bulk, and more especially in their 

 diameter being larger. 



2. In their colour, which is usually darker. 



3. In being covered externally by a large number of 

 imbricated bracts (or hypsophyllary leaves), which 

 together form the general involucre. 



Select a very young capitulum that is, one in which 

 these characters can be recognized, but are not as yet 

 very pronounced and, having removed the largest 

 external bracts, cut from it median longitudinal 

 sections : treat with potash for about ten minutes, and 

 mount in glycerine : observe with a low power 



1. That in outline and general arrangement of parts 

 the sections resemble those of the vegetative bud, but 

 that the apical cone is broader, and more flat. 



2. That the surface of the cone has an irregular 

 outline, owing to the formation of a series of appen- 



