680 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



flower is mature they are in a great state of tension, so that when a bee 

 alights upon them the weight of the insect disturbs the equilibrium and 

 the petals drop vertically (b) by the curving of the claws (c). 



In the case of the Medicks, it is the staminal tube (fig. 292 c), and not 

 the petals, which constitutes the spring. This curves upwards, forming a 

 semicircle or more (c). In both flowers, the bee will be violently dashed 

 with pollen. In figure 292, a represents a flower seen from the front 

 before, and b the same after the explosion. 



In the Barberry, the stamens, from having been at first spread out 

 upon the expanded petals, if lightly touched, spring forward upon the 

 pistil. 



In the male flower of Nettles, the stamens are incurved in bud ; but 

 as soon as the four sepals open out, the four stamens spring out, violently 

 recurving themselves (fig. 293). A little plant allied to the Nettle does 

 the same, and as the pollen is ejected into the air it has acquired the 

 name of " Powder and Shot." 



In Rock-roses (Helianthemum) the numerous stamens, if gently 

 gathered up between the first two fingers and the thumb, slightly com- 

 pressed, and then liberated, instantly spread themselves out gently upon 

 the petals. 



Tensions and Elasticity. — The force of tension is well exhibited in 

 the florets of the so-called "flowers " of the large family of Composites. 

 This name is derived from the fact that the " flowers " or " heads" of 

 these plants are not simple, but aggregations of florets, each of which 

 has five stamens attached to the tube of the corolla by their filaments 

 (fig. 294). 



The fine anthers are long, and instead of being free are united side 

 by side (a), so that they form an elongated cylinder or tube, held erect 

 upon the five filaments as supports (6), which arise from their insertions 

 on the corolla (c). These are highly elastic. The tips of the anthers in 

 the unopened stage of the floret bear triangular flaps above the anther- 

 cells, which close over the end of the tube. The style of the pistil passes 

 up the middle of this anther-cylinder, so that its extremity abuts against 

 the closed end of it. The stigmas, when fully developed, consist of two 

 flat branches called "style-arms" (see figure), having the " stigmatic " 

 surfaces on the inner side, being pressed together as long as they are 

 within the tube. 



At the period of expansion of the corolla, the style is continually 

 elongating, and, by pressing upwards against the closed summit of the 

 anther-tube, stretches the elastic filaments to their fullest extent, so that 

 as soon as the anther-tips give w^ay the filaments, by their contraction, 

 drag the anther- cylinder downicards, while the style protrudes out of the 

 top, elevating the stigmas into the air. In so doing the pollen is swept 

 out of the cells and brought up to the air. The grains of pollen thus 

 ultimately appear aggregated on or about the summit of the elevated 

 style. 



It is not until the style is well through the anther-tube that the two 

 branches of the stigma diverge, looking like a pair of rani's horns, and 

 exposing their stigmatic surfaces, which are thus ready to receive the 

 pollen conveyed by insects from some other flower. 



