476 



APPENDIX. 



(Fig. 15). The pollen-grains, carried by the wind, are 

 brought directly to the micropyle, which contains a gummy 

 fluid, and as this fluid dries up and contracts the grains are 

 drawn down to the surface of the nucellus. Then the cone 

 closes up and grows much larger owing to increase in thick- 

 ness of the axis and of the ovule-bearing .scales. Pollination 

 occurs in May or June, and during the ensuing winter the 

 cones are green and closed up not to open again until the 

 are ripe. 



MICRQPYLE 

 NUCELLUS 



ARCHEGONIA 

 / PROTHALLUS 

 .- INTEGT. 



OVULIF. SCALE 

 CARPEL SCALE 



Pig. 15. Ovule of Pine. 

 (Longitudinal section about the time of fertilisation.) 



About a year after pollination has been effected, the actual 

 process of fertilisation occurs. In the meantime changes 

 have been going on inside the ovule. A cell at the upper end 

 of the nucellus (the end nearest the micropyle) grows large 

 and then divides up and forms a mass of tissue often called 

 the " primary endosperm " in which several archegonia are 

 formed at the end nearest the micropyle. These archegonia 

 differ from those of the Fern in having very short necks and 

 in being buried below the nucellus, instead of projecting 

 freely from the surface of the plant. Then the hitherto 

 dormant pollen germinates, sending pollen-tubes (Fig. 16) 

 down through the nucellus, and carrying the male fertilising 



