POLLEN, OR FLOWER-DUST 99 



acting* very much like the young root of a ger- 

 minating seed as it penetrates the soil, the 

 difference being that, instead of growing down 

 into the soil, it penetrates the stigma and con- 

 tinues its course through the spongy tissue until it 

 reaches the ovary or seed vessel, guided by 

 various contrivances such as delicate hairs or 

 papillae. The pollen-tube, formed from the elastic 

 tissue of the intine, reaches an extraordinary 

 length in comparison with the size of the grain 

 before it reaches the ovules, which after fertilisa- 

 tion are destined to become fruitful seeds. Here 

 the pollen-tube opens, and the contents of the 

 polltrn-grain, including a nucleus, are passed 

 through the tube into the embryo seed, after 

 which the seed develops by a natural growth. 



Fig. 63 shows a section of a portion of the 

 stigma of the evening primrose, with the ger- 

 minating pollen-grains in position. These pollen- 

 grains are flattened and of triangular form, some 

 of them being shown in Fig. 64, and it will be 

 seen in the former example that the grains emit 

 their tubes at the corners, and these can readily be 

 seen insinuated amongst the cells of the stigma 

 and its neighbouring tissues. 



In Fig. 65 is shown another example of a flat 

 triangular form of pollen-grain from a common 

 garden Godetia, which belongs to the same family 



