24 ELEMENT! OP STRUCTURAL BOTANY. 



four sepals. The corolla is polypetalous, and of four 

 petals. The stamens (Fig. 28) are six in number, and if 

 you examine them attentively, you will see that 

 two of them are shorter than the oilier four The 

 stamens are consequently said to be tetradynamous. 

 But if there had been only four stamens, in two 

 sets of two each, they would have been called 

 didynamous. The stamens are inserted on the receptacle 

 (hypogynous). The pistil is separate from the other parts 

 of the fiower (superior). 



30. To examine the ovary, it will be better to select a 

 ripening pistil from the lower part of the peduncle. 

 It is a flat body, shaped something like a heart (Fig. 29), 

 and having the short style in the notch. A ridge divides 

 it lengthwise on each side. Carefully cut or pull away 



the lobes, and this ridge will remain, pre- 

 senting now the appearance of a narrow 

 loop, with a very thin membranous parti- 

 tion stretched across it. Around the edge, 

 on both sides of the partition, seeds are 

 suspended from slender stalks (Fig. 30). 



Fig. 29. Fig. so. There are, then, two carpels united together, 



and the pistil is, therefore, syncarpous. 



31. Shepherd's Purse is a type of a large and important 

 Order, the Crurjferte, or Cress Family. Other common 

 examples, which should be studied and compared with 

 Shepherd's Purse, are the garden Stock (single flowers an- 

 best for examination), Water-Cress, the yellow Mustard 



Fig. 28. The same, with calyx and corolla removed. 



Fig. 29. Ripened pistil of Shepherd's Purse. 



fig. 30. -The same, with one side removed to show the 



