234 



ORGANOGRAPHY. 



spiral vessels, and which is itself covered hy thin epidermal 

 tissue. The epidermis occasionally presents stomata and hairs ; 

 these hairs are sometimes coloured, as in the Spiderwort (Tra- 

 descantia virginica), and in the Dark Mullein {Verhascum ni- 

 grum). 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 component parts. 



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

 lars ; a few of the more important modifications of which 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 

 generally tapers in an almost imperceptible manner from the 

 base to the apex, when it is described as filiform, as in the Eose ; 

 or if it is very slender, as in most Sedges and Grrasses, it is ca'pil- 

 lary {figs. 486 and 488). In the latter case, the filament, instead 

 of supporting the anther in the erect position as it usually does, 

 becomes bent, and the anther is pendulous. At other times the 

 filament becomes enlarged, or it is flattened in various ways. Thus 

 in some cases, it is dilated gradually from below upwards like a 

 club, when it is clavate or cluh-shaped, as in Thalictrum ; or it is 

 slightly enlarged at the base, and tapers upwards to a point like 

 an awl, as in the FloM'ering Eush {Butomus umbellatus) ; in other 

 cases it is flattened at the base, the rest of the filament assu- 

 ming its ordinary rounded form, as in Tamarix gallica{fig. 489) 

 and species of Cmnpanula {fig. 490) ; or the whole of the fila- 



Fig. 488. 



Fig. 489. Fig. 490. 



Fig. 488. Alocusta of Wheat {Triticnm) consisting of several flowers, the 

 stamens of which have very long capillary filaments, and versatile 

 pendulous anthers. The anthers are hifurcated at each extremity, and 

 resemble somewhat the letter x in form. Fig. 489. Three of the sta- 

 mens of the Tamarix gallica, with their filaments flattened at the base 

 and united with one another. Fig. 490. Pistil of a species of Campa- 

 nula, with a solitary stamen arising from the summit of the ovary. 

 The filament is flattened. 



