STRUCTURE OF A FLOWER 



107 



parts of the flower. They are really to be regarded as spore- 

 bearing leaves or sporophylls. 



Each stamen consists usually of a long stalk or filament (/), 

 bearing an anther (a) at its extremity. The anther is a bilobed 

 structure, and each lobe contains two chambers, or pollen sacs, 

 in which the pollen grains (p) are formed by the division of 

 mother cells into fours, just as the spores of an ordinary fern 

 are developed within the spo- 

 rangia. The pollen sacs are, in 

 fact, nothing but sporangia 

 and microsporangia, because they 

 contain microspores. 



The pistil is formed of a vary- 

 ing number of carpels, which, 

 either singly or united, give rise 

 to a closed chamber below, the 

 so-called ovary 1 (F), surmounted 

 by a longer or shorter style (g), 

 ending above in a rounded viscid 

 surface, the stigma (?i). In the 

 interior of the ovary, attached 



to the carpels, are developed the FIG. _53. Diagram of a typical 

 ovules (S), which are nothing 

 but sporangia (megasporangia) 

 enclosed each in a double enve- 

 lope (i). In each ovule a single 

 embryo sac or megaspore (em) 

 is produced. Only one ovule 

 is represented in the diagram, but there are usually a large 

 number in each ovary. 



Having thus briefly described the parts of the sporophyte 

 with which we are immediately concerned, we must turn our 

 attention for a few moments to the gametophyte. The male 

 gametophyte, which never consists of more than a very small 

 number of cells, is developed from the pollen grain or microspore. 

 This latter is at first a perfectly typical unicellular spore, 

 with a single nucleus surrounded by cytoplasm, and the whole 

 enclosed in a thick protective cell-wall often ornamented with 

 microscopic sculpture of various patterns. The commencement 



1 This is a very unfortunate name because the structure in question is an entirely 

 different kind of organ from the ovary of animals. 



Flower in vertical Section. 



(From Vines' " Botany.") 

 a, anther ; em, embryo sac ; E, ovum ; 

 /, filament of stamen ; F, wall of 

 ovary ; g, style ; i, integument of 

 ovule ; K, corolla ; Ke, calyx ; n, 

 stigma ; p, pollen grains ; ps, pollen 

 tube ; S, ovule. 



