ORGANS OF REPRODUCTION. 241 



Mercurialis, when it is dioecious. In some cases, as in many- 

 Palms and Pellitory (Parietaria), both staminiferous, pistillifer- 

 ous, and hermaphrodite flowers, are situated upon the same 

 individual, in Avhich case the plant is called polygamous. 



Like the calyx and the corolla, the stamens and pistil are 

 considered as homologous with leaves, but they generally pre- 

 sent much less resemblance to those organs than the floral 

 envelopes. Their true nature is shown however, by their 

 occasional conversion into leaves, and by other circumstances 

 which will be described hereafter when treating of the General 

 Morphology of the Flower. They make their flrst appearance 

 upon the upper part of the axis or thalamus as small cellular 

 processes, in the same manner as the floral envelopes. 



1. THE STAMENS OR ANDRCECIUM. 



The stamens constitute the whorl or whorls of organs situated 

 between the corolla on the outside and the pistil on the inner 

 (figs. 421 and 422), and form collectively the androecium or 

 male organs of the flower. Each stamen consists generally of 

 a thread-like portion or stalk, called the filament (fig. 4t'23,/). 

 which is analogous to the petiole of the leaf, and of a little 

 bag or case, a, which is the representative of the blade, called 

 the anther, which contains a powdery matter termed the pollen, 

 p. The only essential part of the stamen is the anther contain- 

 ing the pollen, and Avhen this is absent, as the 

 stamen cannot then perform its special func- Fig. 489. 

 tions, it is said to be abortive or sterile. When 

 the filament is absent, which is but rarely the 

 case, as in the Arum (fig. 489), the anther is 

 described as sessile. 



1. The Filament. — In its structure the fila- 

 ment consists, 1st, of a central bundle of spiral 

 vessels which is usually unbranched and termi- 

 nates at the connective of the anther ; 2nd, of 

 cellular tissue which surrounds the central of tiie A^rum! 

 bundle of spiral vessels, and which is itself consisting sim- 

 covered by a thin epidermal layer. The epi- thers'essileupoii 

 dermis occasionally presents stomata and hairs. ^^^ thalamus. 

 These hairs are sometimes coloured, as in the 

 Spiderwort (Tradescantia), and in the Dark Mullein (Verbas- 

 cum nigrum). The structure of the filament is thus seen to be 

 strictly analogous to that of the petiole of a leaf, which presents 

 a similar disposition of its comyjonent parts. 



The filament varies in form, length, colour, and other parti- 

 culars ; a few of its more important modifications in these 

 respects will be now alluded to. 



Form. — As its name implies, the filament is usually found in 

 the form of a little thread-like or cylindrical prolongation which 



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