498 NATURAL HISTORY OF PLANTS. 



ally often a little before anthesis. In the bud the filament is 

 involute and more or less coiled, with the face of the anther applied 

 to the concavity of the corresponding sepal. But on expansion it 

 uncoils by its elasticity 1 directly the anther is free to quit the central 

 body that hooked it down, and becomes suddenly straight, the 

 anther-cells often opening simultaneously to shoot out the pollen. 2 

 The female flower (figs. 536-538) bears on its convex receptacle 



Urtiea pilulifera. 



Fig. 536. 

 Female flower (±). 



Fig. 537. 

 Diagram of female flower. 



Fig. 538. 



Long, section of female 

 flower. 



four sepals, nearly free or united for a variable distance, imbricate- 

 decussate as in the males, but often with the two pairs dissimilar, 

 the lateral two being usually larger and more concave or carinate 

 than the antero-posterior, and sometimes also dissimilar to one 

 another, rendering the perianth slightly irregular. In the centre ol 

 the flower is a unicarpellary gynseceum formed of a free ovary ; the 

 terminal style is often very short, or at once divides into a large 



1 This is dne to a peculiar property of its tissue, 

 which gives it a great elasticity. " The filament 

 itself describes a large arc, occupying the space 

 between the lobes of the anther above ; it is often 

 transversely notched on its concave side, so as to 

 allow of this forced inflexion. When at last 

 anthesis takes place, and the perianth-leaves 

 scarcely begin to diverge, the filament, by the 

 mere turgescence of its cells, suddenly springs 

 up from the position in which it was hithei'to 

 mechanically retained." (Wedd., Mon., 27.) 

 " if on gathering the flowers this phenomenon is 

 at once produced, it must not be supposed that 

 the shock has excited the irritability of the 

 stamen ; it has merely freed it from its prison. 

 And though the singular structure of the fila- 

 ment, its transverse folds and vertebralike 



articulations, may at first sight appear the indices 

 of a special vital action, it will soon be seen that 

 this arrangement is not the cause of the phe- 

 nomenon, but the result of the forced flexure 

 during its growth." [H. Bn., Des Mouo. dans 

 les Org. Sex., &c. (Far., 1856), 39.] The facts 

 observed in the Fellitories, whose stamens do not 

 always possess these elastic filaments, will enable 

 us to modify this assertion to some extent. 



2 " Spherical, with three umbilici, each sur- 

 rounded by a halo ; outer membrane transparent," 

 in Urlica nrens and Parietaria erecta ; and the 

 same with four pores in Bvehmeria caudata, 

 according to H. Mom (in Ann. Sc. 2?at., ser. 2, 

 iii. 313). Weddell (Blonogr., 27) says that the 

 pollen is globular. 



