FertiHsation of Gymnosperms 129 



there are several cells which enlarge and form secondary 

 embryo-sacs or corpuscula. These split up into two cells, the 

 upper or neck cell breaking up into several, which form a tube 



Fig. 24g. —Fertilisation of Cnpressus sent- 

 pervirens (ConiferEe). I. A pollen grain 

 with its two cells : a^ extine ; b^ intine. 

 II. Pollen grain in which the pollen-tube, 

 Ct has been formed. 



Fig. 250. — Fertilisation of Abies 

 excelsa. : p, pollen grains ; ps, 

 pollen-tubes ; <:, two corpuscules 

 in the embryo-sac, e. 



or neck leading into the lower cell, which enlarges, forming the 

 oosphere. The pollen-tube grows down to the oosphere, fer- 

 tilising it and causing it to break up into a pro-embryo or sus- 

 pensor, which forces its way through the embryo-sac, and at 

 the end of which the embryo is produced. 



Recent investigations seem to point out that in the fertilisation of 

 Angiosperms there is a certain 

 approach to this process as seen 

 amongst the Gymnosperms. In 

 ' Nature ' for July 1879 an inte- 

 resting paper appeared, giving 

 an account of the researches of 

 Messrs. Strasburger and Elfving 

 at Jena. They treated pollen 

 grains with osmic acid so as to 

 render the contents more visible, 

 and then they grew them arti 

 flcially in sugar solutions. In a number of the cases observed there seemed 

 to be a breaking up into two or three cells previous to the emission of 



K 



-Pollen of Tulip, A, 

 Flowering Rush, c. 



