THE FLORAL DEVELOPMENT OF HELIANTHUS ANNUUS. 121 



the form of a slightly rounded cushion, over-arched by the modified 

 leaves or bracts of the involucre, or what was at one time regarded 

 as the common calyx of the compound blossom. 



Upon the surface of this cushion or receptacle, the florets, with 

 their subtending bracts, are developed. The earliest appearance 

 which they present in common with all young organs, is that of a 

 hemispherical tubercle ; those nearest the circumference of the 

 capitulum are the first to appear, development than proceeding in 

 centripetal order. The tubercle, however, speedily loses its 

 hemispherical form, and appears as shown in section in Fig. 1, being 

 a circular protuberance with a flattened summit. The free edge now 

 begins to grow more rapidly, and a hollow upper surface is the 

 result, the margin of which is the commencement of the future 

 corolla (Fig. 2). On the rudimentary corolla five rounded papillae 

 arise — these are its lacinise or divisions — and growth still being 

 more vigorous on the exterior, causes an over-arching of the corolla, 

 so producing the valvate astivation which is one of the character- 

 istics of Composites. An early stage of this is shown in Fig. 3. 



It is at this period of development that we find the first indica- 

 tion of the stamens as five small projections at the internal base of 

 the corolla, and alternating in position with its divisions. This is 

 shown in section in Fig. 3. The Anthers of all Composites are 

 syngenesious, or so united as to form a tube, the filaments being- 

 free. This is brought about by the whole of the tissue, on which 

 the staminal whorl originates, growing upward, so that what was 

 at first but five papilla? is now a cylinder with five somewhat conical 

 projections on its upper end. The tissue after a time separates near 

 the base, at intervals corresponding with those which originally 

 divided the stamens from each other ; growth is arrested in a tan- 

 gential direction, thus forming the Anthers, but proceeds vertically 

 at the original points of emergence, till the filaments are developed. 



Next in order arises the so-called calyx, as two projections at the 

 base of the corolla, assuming at maturity the appearance of minute 

 scale-like leaflets, or, as Sachs describes them, " sub-paleaceous 

 Awns." If these are to be regarded as referable to the calyx, we 

 note how late is their development — that which should have been 

 first only just precedes, or is synchronous with the fourth whorl, for 

 at this time we observe the first appearance of the pistil in the form 

 of two semi-lunar prominences at the base of the stamens (Fig. 4) ; 

 both the leaflets and the carpellary leaves of the pistil being arranged 



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