CHAPTER XL 



THE ANTHER AND POLLEN. 



Development of Pollen Sporogenous tissue Pollen mother-cells 

 Pollen-sac Pollen-grain Pollinia Sculpturing of walls 

 Changes in contents Pollen of Gymnosperms Shapes and 

 sizes of pollen-grains Distribution of pollen by wind, insects, 

 water, &c. Germination of pollen-grain Pollen-tube Vegeta- 

 tive and Generative Nuclei Homologies Spermatozoids 

 Exine and Intine Markings on the walls Comparison of 

 pollen-grain to a spore Germination Comparison with the 

 spores of Cryptogams. 



A TRANSVERSE section of the very young stage of 

 a stamen, which frequently grows far more rapidly than 

 the petals, shows it to be composed entirely of embryonic 

 tissue, but soon after the distinction between anther and 

 filament is established a transverse section of the former 

 shows that several tracts of cells can be made out. An 

 outer layer of cells is already marked out as the epidermis, 

 and in the central part of the connective may be seen 

 a strand of cells remarkable as dividing oftener in the 

 vertical direction than across it, thus forming a strand of 

 tissue which will constitute the slender vascular-bundle 

 continuous from the floral axis through the filament. 



The rest of the anther usually shows a more or less 

 four-lobed outline, in each lobe of Avhich one to three or 

 more cells are remarkable for their bright contents and 



