HISTOLOGY OF ANGIOSPERM STEM, ROOT, ETC. 127 



general outline of the section and compare with an entire 

 anther; there are three longitudinal grooves one along 

 the middle of the inner face and one along either flank, 

 while along the middle of the outer face there is a whitish 

 band, the connective. 



With high power, note (1) the tissue of the connective, 

 with a vascular bundle in a nearly central position ; 

 (2) the four pollen-sacs, two on either side, containing 

 the pollen-grains ; (3) the epidermis covering the entire 

 anther and consisting of small cells along the outer side 

 of the connective stomata may be seen cut through, and 

 at the points where the two pollen- sacs on either side of 

 the anther meet there is a band of large epidermal cells ; 

 (4) the fibrous tissue, consisting of cells with the walls 

 thickened by spiral or annular bauds arranged transversely 

 to the long axis of the anther. Below the epidermis of 

 the pollen-sacs this tissue consists of a well-defined layer 

 of large cells ; along the inner side of the anther there are 

 several layers of smaller cells ; while at the point where 

 the partition between the two pollen- sacs meets the anther- 

 wall the fibrous tissue is absent (dehiscence line). 



Also examine longitudinal sections of an anther, cut parallel 

 to the plane of flattening. Starting with a surface section of the con- 

 nective, note the numerous stomata in the epidermis. A section a 

 little deeper will show the vascular bundle of the connective, with 

 its xylem vessels, also the thickening bands in the cells of the 

 fibrous tissue. 



162. Structure of Pollen-grains. Note the oval or 

 bean-shaped form of the ripe Narcissus pollen-grain ; 

 the outer surface shows granular thickenings. With 

 iodine, or (better) with acetic methyl green, note the two 

 nuclei one spindle-shaped and the other spherical. Pol- 

 len-grains may be rapidly cleared and made transparent 

 by treatment with either chloral hydrate or carbolic acid. 



For comparison with Narcissus, examine the pollen -grains of 

 various other plants, and note the great differences in size, form, 

 surface sculpturing and outgrowths, etc. A good selection would 

 be the following : Mallow or Hollyhock, Marrow or Cucumber, 

 Broad Bean, Crocus, Chicory, Wallflower, Rhododendron, also the 

 pollinia of Orchis. 



