DEVELOPMENT OF PLANTS 



379 



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, i). The microsporo- 

 phylls, 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- 



FIG. 261 A. Flower and sporophylls of Angiosperms: i, flower of Sedum 

 with leaf-like perianth, p; microsporophylls, 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 breaking 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 m, 

 spore mother cells. The large cells surrounding the mother cells are nour- 

 ishing cells, known as the tapetum, and disorganize as the spores mature. 

 At the right a mother cell forming four microspores, the upper one being 

 characteristic of dicotyledons and the lower of monocotyledons. 



