NATURE OF PLANTS 



109 



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

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

 formation of the seed. The stamens consist of a lobed sack or 

 anther which is usually supported upon a stalk or filament (Fig. 

 74, C). If a young anther is cut across four cavities, contain- 

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

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

 grains, are minute cells, provided with a cell wall often variously 



Fig. 74. Flower of the stonecrop, Sedum: A, bud stage of flower — ca, 

 calyx showing three sepals. B, open flower — p, petals of corolla; 5, stamens; 

 c, pistils or carpels. C, stamen, consisting of a four-lobed anther supported 

 on delicate stalk or filament. D, pistil or carpel — 0, ovary; s, style which 

 terminates in a small knob or stigma. E, longitudinal section of ovary showing 

 row of ovules attached to wall of ovary. F, cross-section of ovary, ovules in 

 two rows. 



sculptured and contain a nucleus and protoplasm like an ordinary 

 cell (Fig. 79). At maturity the anthers break open in a manner 

 that varies in different plants, exposing the microspores to the 

 air (Fig. 75, B). The pistil or carpel is quite different in char- 

 acter. At or near the top is a more or less modified part, the 



