126 THE FLORAL DEVELOPMENT OF HELIANTHUS ANNUUS. 



form of the other, although in size, outline, and structure such a 

 great divergence has taken place ; and continuing the series, we 

 find bracts in which further modification has taken place, and which 

 will, so far as structure is concerned, demonstrate that these diminu- 

 tive scales, whether regarded as sepals or not, are certainly not 

 Trichomes. 



Taking now the bract (Fig. 18), we find it abundantly supplied 

 with chlorophyll, but which gradually diminishes in quantity as the 

 bracts get farther away from the circumference of the capitulum ; 

 this is shown in the figures, the shaded portions representing the 

 decreasing surface occupied by it. Another feature to be observed 

 is that they become greatly reduced in substance, and at last scale- 

 like in appearance, the only part containing chlorophyll being that 

 which, projecting above the floret, is exposed to the influence of 

 light. Only one vascular bundle is present, that representing the 

 mid-rib ; stomata are also absent, except upon the green portions ; 

 the chlorophyll, the vascular system, and the stomata disappearing 

 together, and were it not that some portion of the bracts were still 

 exposed to the influence of light, we should find them in all respects 

 as rudimentary as the two leaflets under consideration ; as it is we 

 find they nearly approach each other. 



Taking then the facts above cited as to origin and structure, 

 together with the circumstance that the subtending bracts of the 

 florets do not differ much in the latter particular, I think we must 

 conclude that they belong to Phi/ Homes rather than Trichomes, and 

 if so, we can scarcely help referring them to the calyx, in spite of 

 their retarded development and want of symmetry ; for if we regard 

 them as bracts joined to the ovary, as Duchartre suggests, the same 

 difficulty as to retardation presents itself, but in a greater degree. 



EXPLANATION OF PLATE IX. 



b. bract. co. corolla. s. stamens. cp. carpels. d. disc 



p. pistil. sp. sepals. a. apex. /. funiculus. pr. primine. 



n. nucleus. ov. ovary. sic. ovule. v. vessel. 



Figs. 1 — 9. Development of Florets; 6, Transverse section of fig. 7; 

 dotted line, Fig. 7, position and form of sepals. 



„ 10 — 16. Development of ovule j 14 — 16, development of primine 



and nucleus. 

 „ 17. Sepal, showing position of rudimentary fibro-vascular 



bundles. 

 „ 18 — 22. Floral Bracts from one capitulum ; shaded portion indicates 



extent of surface occupied by chlorophyll. 



