GENERAL OBSERVATIONS. 25 



Angiosperm, both in anatomical and physiological observations, 

 owing to the fact that it exhibits, par excellence, what is regarded 

 as a normal structure little modified by specialization for any 

 peculiar environment. 



Not only is Helianthus a leading type of the Compositae which 

 hold the highest position among Angiosperm families, but amongst 

 this family it flourishes in the best stations, in which sunlight, air 

 and water-supply are perhaps at an optimum for modern vegetation, 

 The very fact that it is as near an approximation to the typical 

 Angiosperm as can perhaps be obtained, suggest that the phenomena 

 of growth exhibited by it will also be normal, and from the time 

 of Braun to that of Schwendener it has afforded a classical example 

 of spiral phyllotaxis. 



As is well known, the plant forms a main axis of only annual 

 duration, growing 7-8 feet, or in special eases even 15 feet, during 

 the summer months ; the leaves are typical in character, and are 

 borne spirally with a divergence to which, since the stem has 

 passed through a very active zone of elongation, the application of 

 any fractional value must be purely empirical, but it would be 

 generally said to range between § and ^. In the open, the stem 

 grows erect without torsion, and terminates in the main inflor- 

 escence. Branches are normally developed to the second degree, and 

 these again terminate in inflorescences similar to the terminal one, 

 but on a progressively smaller scale. The vegetative leaves pass 

 gradually by reduction into an involucre of leaf-base scales (fig. 14) ; 

 and contemporaneously with 1;he formation of these, the axis 

 broadens out, elongation practically ceases, but lateral extension is 

 very considerable, so that the capitulum disk approaches a level 

 surface and the whole energy of growth is directed radially. 



As in Gynara Scolymus, the involucral scales exhibit therefore 

 the phenomenon of a " rising phyllotaxis," and it is futile to at- 

 tempt to give it any fractional value until the broadest diameter 

 of the inflorescence is reached. Here the leaf -members become 

 fertile scaly bracts and subtend the florets of the disk; the 

 sterilized ray-florets being subtended by the innermost series of 

 the large scales. The fertile bracts mark out rhomboidal areas 

 and the enclosed flower-primordia are circular in section: 



