GROWTH OF THE POLLEN. 79 



charged their contents, which in some man- 

 ner fertilized the ovules or young seeds. In 

 1823 an Italian, Amici, perceived that the 

 grains of pollen upon the stigma of an Afri- 

 can plant changed into tubes, which he des- 

 ignated the pollen tubes. Four years later, 

 the celebrated Brongniart confirmed the ob- 



Fig. 66. 



servation of Amici, and found that the tubes 

 were produced in many plants, and further- 

 more that they penetrated the soft tissue of 

 the stigma. It is now known that the pollen 

 grain germinates after it falls upon the 

 stigma, and sends a minute tube down 

 through the stigma and style, finally penetra- 

 ting the ovule or seed-forming body. One 



