102 



NATURE I »F THE SP< >k< iPHYLLS 



51. The Structure of the Sporophylls.- Let us examine the 

 structure of these organs and see how they co-operate in the 

 formation of tin- seed. The stamens consist of a lobed sack or 



Fig. 74. Rower of the stonecrop, Sedum: ./. bud stage of Bower— 

 ((/, calyx showing three sepals. />'. open flower—^, petals of corolla; s. 

 stamens; c, pistil- or carpels. ('. stamen. o»n>i>tinn of a four-lohcd anther 

 supported on delicate -talk < .r filament. /'. pistil "r carpel — o, ovary; s. 

 style which terminates in a small knob or stigma. /:'. longitudinal section 

 of ovary showing i"\\ of ovules attached t" wall of pvary. F, cross-section 

 <>i ovary, ovules ifl two rou s. 



anther which is usuall) supported upon a stalk or filament t Fig. 

 7). ( 1. [fa young anther is cut across four cavities, contain- 

 ing minute or dust-like grains, the microspores, will be seen 

 75, A). The microspores, also called pollen spores or 

 grains, arc minute cells, provided with a cell wall often variouslj 

 sculptured and contain a nucleus and protoplasm like an ordinary 

 cell ( Fig. 7' 1 1 . \t maturity the anthers break open in a manner 

 that varies in differenl plants exposing the microspores to the 

 air (Fig. 75. B). The pistil or carpel is quite differenl in 

 character. At or near th< top is a more or less modified part, 



