234 SHEPHERD'S PURSE. 



iii. The fibro-vascular bundle, comparing its tis- 

 sues with those in the stem bundles. 



b. The two theccz, each consisting of two valves. 



c. The wall of the valves, consisting of 



i. The epidermis. 



ii. The endothecium> an elastic inner row of spir- 

 ally thickened cells. 



d. Draw a section of a theca showing its tissues. 



e. The pollen. Note 



i. The surface of the wall. 



ii. The two layers of the wall : the extine col- 

 ored and with thin spots ; the intine thin and 

 colorless. 



By careful pressure upon the cover glass, there can be 

 seen 



iii. The intine unbroken, but protruding through 

 one of the thin spots in the extine, the 

 true character of the wall becoming thus very 

 obvious, 

 iv. The minutely granular contents. 



4. The pistil. Mount a slice from the surface of the 

 stigma and also a transverse section of the ovary, both 

 cleared with potash, and note 



a. The stigma. 



i. Its surface, with pollen tubes sometimes pene- 

 trating it. 

 ii. Draw. 



b. The ovary. 



i. The epidermal cells, 

 ii. The character of the mesophyll. 

 iii. The fibro-vascular bundles, their position and 



tissues, 

 iv. The structure of the placentae. 



