410 CONTENTS OF THE POLLEN-TUBES. 



two sides, so as to come in contact with the con- 

 ducting tissue " through which the pollen-tube con- 

 taining the fertilizing matter forces itself In some 

 plants, " the surface of the conducting tissue actually 

 elongates and stops up the mouth of the ovule while 

 fertilization is taking effect. In plants of the genus 

 Helianthemum the foramen is at the end of the 

 ovule most remote from the hilum ; and although 

 the ovules themselves are elevated upon cords much 

 longer than are usually met with, yet Brongniart 

 ascertained that at the time when the stigma is cov- 

 ered with pollen, and fertilization has taken effect, 

 there is a bundle of threads, originating in the base 

 of the style, which hang down in the cavity of the 

 ovary, and, floating there, convey the influence of 

 the pollen to the points of the nuclei." 



As was stated by Herbert, the process of fertiliza- 

 tion is very slow, and it is often a great while (sev- 

 eral days, or even weeks, after the fecundation of the 

 stigma) before the pollen-tube reaches the foramen. 

 Yet the life of the corolla, and the other parts of the 

 flower, will be finished long before this time. The 

 membrane immediately surrounding the embryo is 

 called the amnion. Comparative mystery enveloj)es 

 the operation which takes place in this amnionic sac. 



Schleiden maintains that the microscopic observa- 

 tions of Fritsche prove that the molecules which 

 exist in the pollen and its tubes are not animalcular, 

 from the fact that they were undisturbed by alco- 



