MOKl^HOLOGY OF REPRODUCTIVE ORGANS 187 



a stalls called the caudicle (fig. 392, c), whicli adheres commonly 

 at the period of dehiscence to one or two little glandular masses 

 oallei retinacula {figs. 394, a, and 392, r, r). These are placed 

 on the upper surface of a little projection called the rostellum, 

 situated at the base of the anther. 



PoUeu-gralns are found of various shapes. The most 

 common forms appear to be the spherical (fig. 384) and oval 

 (fig. 385) ; in other cases they are polyhedral, as in Chicory 

 {Cichoriiim Intijhus) and Sonchus palustris, or triangular with 

 the angles rounded and enlarged (trigonal), as in the Evening 

 Primrose (CEnothera biennis) and plants commonly of the 

 order Onagracea3 (^i;. 390), or cubical as in Basella alba, or 

 cylindrical as in Tradescantia virginica, while in Zostera they 

 are thread-like or of the form of a lengthened tube or cylinder ; 

 other shapes also occur. The form of the pollen is materially 

 influenced according as it is dry or moist. Thus the pollen- 

 grains of the Purple Loosestrife (Lythruni Salicaria) and some 

 species of Passion-flower are oval when dry, but when placed in 

 water they swell and become nearly globular. Again, when 

 spherical pollen-grains are exposed to the air for some time they 

 frequently assmne a more or less oval form. 



In size, poUen- grains vary from about ^J^ to ^^^ of an inch 

 in diameter ; their size, however, like their form, is liable to vary 

 according as they are examined in a dry state or in water. 



d. The Ggncerium or Pistil. 



The gynocium, or pistil, occupies the centre of the flower, 

 the andrceoium and floral envelopes being arranged around it 

 when they are present ; the floral envelopes alone in the 

 pistillate flower ; while it stands alone when the flower is 

 pistillate and naked. The gynceciuni consists of one or more 

 modified leaves called carpels, which are either distinct from 

 each other, as in the Crowfoot ( fig. 366) ; or combined into one 

 body, as in the Primrose (fig. 361) and Tobacco (yigf. 897). 

 When there is but one carpel, as in the Pea {fig. 406), Broom 

 (fig. 396), and Leguminous plants generally, the pistil is said to 

 be simple ; when there is more than one, it is described as com- 

 pound whether they are distinct from each other, as in the Crow- 

 foot (fig. 366), or combined into one body, as in the Tobacco 

 (fig. 397) and Primrose (fig. 367). 



Before proceeding to examine the gyncecium or pistil 

 generally, it is necessary to describe the carpel, of one or more 

 of which organs it is composed. 



