346 



SI'oROPHYLLS OF ANGIOSPERMS 



The sporophylls, like all organs of the plant, show a wide range 

 of variation and they are generally associated with more or less 

 modified leaf-like organs which serve to protect them. These 

 leaf-like organs are known as the floral envelope or perianth and 

 doubtless arose in many forms through the sterilization and modi- 

 fication of the sporophylls (Fig. 261 A, 1). The microsporo- 

 phvlls, often called stamens, usually consist of a stalk or fila- 

 ment and a four-lobed spore-bearing part, the anther (Fig. 261 A, 

 2). In cross-section, the anther is seen to consist of four spo- 

 rangia in which the microspores originate in tetrads as in the 



Fig. 261.-/. Flower and sporophylls of Angiosperms : 1, flower of 

 Sedum with leaf-like perianth, p; mierosporophylls, s; megasporophylls, 

 c. 2, microsporophyll of the buttercup, showing four-lobed anther and 

 filament. 3, diagram of a cross-section of an anther, showing the break- 

 ing down of the tissue about the four sporangia and the beginning of the 

 opening of the anther. 4, one of the sporangia from a young anther, as 

 seen in cross-section — in, spore mother cells. At the right a mother cell 

 forming four microspores, the upper one being characteristic of mono- 

 cotyledons and the lower of dicotyledons. 



