204 



HARDWICKE'S SCIENCE-GOSSIP. 



STUDIES OF COMMON PLANTS. 



No. II. — The Common Sunflower {Hdianthus 



An mats.) 



By E. A. Swan. 



A CAREFUL study of the flower will amply 

 repay the trouble taken. The various parts 

 are beautifully adapted for ensuring fertilization by 

 means of insect agency. Most people are ignorant 

 of the elaborate contrivances by which this is effected. 

 Many look upon ^this humble denizen of our gardens 

 as worthy of but passing notice, yet nothing can be 

 more unreasonable. 



The stalk, as every one knows, supports a flower 

 which consists of, first, several whorls of bracts 

 forming the involucre ; second, one or more whorls 

 of yellow florets constituting the ray ; and third, a 



Each blossom consists of the corolla, which is 

 monopetalous, and ends in five lobes ; within this, 

 the stamens, which are joined half their length from 

 near the top, thus forming a tube ; and, within all,, 

 the pistil, which is cleft at the top. The base of the 

 corolla swells out so as to form a vessel for the nectar, 

 and it is joined by a neck to the achene, from either 

 side of which, at the top, rises what I may call a. 

 short pointed wing. Finally, a rudimentary calyx, 

 partly surrounds each blossom from the bottom of the 

 achene to about midway up the corolla. It is more 

 developed on the outside blossoms, but it is present 

 throughout. It has spines pointing towards the 

 extremity ; so, too, has each wing ; so, too, has the 

 corolla on the outside : and so, too, has the pistil the 

 whole extent of the cleft, but not in the cleft. 



Fig. 133 is a sketch of the uppermost side of a ray 



Fig. 134. 



Fig. 132.— Bracts of Sunflower. 



Fig. 133.— Ray floret. Fig. 136. Fig. 135. 



Fig. 137. Fig. 138. Fig. 139. 



Fig. 140. 



Fig. 141. 



rig. 143. 



Fig. 144. 

 Stamens or 

 sunflower laid 

 open. 



considerable number of blossoms, or perfect florets, 

 called the disc. Each blossom stands on an achene, 

 the covering which contains the seed. 



The general principle of the evolution of the flower 

 from the leaf is well exemplified here. The bracts 

 are clearly modified leaves. I have a specimen 

 before me where the connection can be clearly 

 traced. There a leaf on a short stalk starts from the 

 base of the outermost whorl of bracts. Next it is a 

 bract of ordinary dimensions, and, next that, a bract 

 much larger and having a venation almost like a full- 

 sized leaf. Fig. 132 is a rough outline drawing. Both 

 leaves and bracts are covered on the sides and edges 

 with short spines, all pointing towards the extremity. 

 Some of these spines are pointed, others blunt. I 

 find similar spines, though much smaller, on the ray 

 florets, principally on the under-side, and these ray 

 florets have rudimentary achenes on which they stand. 



floret on its rudimentary achene. It will be noticed 

 that where it joins the rudimentary achene there is a 

 neck formed, and the two edges of the floret meet,, 

 thus making the primary attempt to mould a cup.. 

 My meaning will be clearer by referring to fig. 134, 

 which is the complete achene, wings, neck, cup, anct 

 corolla, drawn, like fig. 133, somewhat about the 

 natural size. Thus we have leaves, bracts, ray 

 florets, and blossoms showing a clear connection. 



Figs. 135 to 143, both inclusive, will help us in- 

 considering the method of fertilization. The outside 

 blossoms are matured first, and, when their work is. 

 done, present the appearance shown in fig. 143. The 

 innermost blossoms are matured last. Fig. 135 shows 

 a blossom not yet opened ; fig. 136, one where the: 

 stamens have just begun to thrust themselves up- 

 wards ; fig. 137, more upwards ; fig. 13S, the pistil first 

 appears, and so on. In an ordinary flower, until the 



