1:20 



A TEXT-BOOK OF BOTANY. 



to their surroundings. But no matter how diversified they may 

 seem in form and structure, they agree in this with possibly one 

 exception, namely, mignonette, that the seeds are produced in a 

 closed carpel. This has been considered, as already indicated, 

 to be the chief difference between the Gymnosperms and Angio- 

 sperms. 



The two groups are further distinguished by several other 

 important characters : ( i ) The carpel or carpels (megasporophyll) 

 is developed into an organ commonly known as a pistil (Fig. 78). 

 This organ consists of three parts, namely, ovary, style, and 

 stigma, the ovary enclosing the ovules. (2) In the Angiosperms 

 the megaspore (embryo-sac) develops a gametophyte which does 



\-j 



Fig. 78. A, longitudinal section through orange flower (Citrus Aurantium) showing 

 stalk (PE); sepals (s) ; petals (p); stamen with filament (F) and anther (A); compound 

 pistil (composed of united carpels) with stigma (T), style (Y) and superior ovary (O) with 

 ovules; disk or nectary (D). B, longitudinal section of a bud of clove (Caryophyllus) 

 showing inferior ovary (O), style (Y), stamens (F), petals (P), sepals (S), nectary (D). 



not give rise to archegonia, but the egg arises directly from the 

 megaspore nucleus by a series of divisions. (3) The Micro- 

 sporophyll (stamen) dift'ers considerably in structure and appear- 

 ance from that of the Gymnosperms. The stamen may be defined 

 as a leaf which bears sporangia (spore cases). It usually con- 

 sists of the following dift'erential parts : filament and anther, the 

 latter consisting of pollen sacs (microsporangia) in which the 

 pollen grains (microspores) are developed (Figs. 78, 79, and 80). 

 (4) In a large number of cases in the Angiosperms there is 

 developed in addition to the sporophylls or sporangial leaves 

 (stamens and pistils) another series of leaves known as floral 

 leaves (Fig. 78). The latter usually are of two kinds, known as 

 sepals and petals. 



