SUBKINGDOM SPERMATOPHYTA 



341 



Fertilization. When the female cone is ready for pollination, the 

 scales separate and the pollen falling upon them sifts into the spaces 

 between them. The scales then close, and very often the upright 

 flower bends over, which probably assists in bringing the pollen upon 

 the apex of the ovule. The integument of the latter is often pro- 

 vided with prominences, which serve to hold the pollen, and a drop 

 of fluid is sometimes excreted, which by its evaporation deposits the 

 pollen upon the apex of the nucellus, where it begins to grow. 



In the Pines the development of the cones requires two years. 

 Pollination is effected in the spring, and the growth of the pollen- 

 tube into the tissue of the nucellus begins ; but growth then stops, 



FIG. 306. A, B, Pinus insignis. A, upper part of gametophyte, with two arche- 

 gonia (X 35). B, lower end of fertilized egg, showing first divisions (X 75). 

 C, young embryo; sus, suspensor ; a;, apical cell. D-F, Taxus baccata. Devel- 

 opment of embryo; x, apical cell; SMS, suspensor. (D, E, X 500; F, X 270.) 

 (D-F, after JAEGER.) 



and is only resumed the following spring, during which the female 

 gametophyte develops and fertilization is effected. The ovule then 

 has the integument hardened, and becomes the seed. 



The development of the pollen-tube is very much like that of the Cycads 

 (Fig. 302), but the male nuclei do not develop into spermatozoids. The pollen- 

 tube pushes through the neck of the archegonium, and in Pinus sylvestris dis- 

 charges its contents, including all the nuclei, into the egg-cell, where one of the 

 generative nuclei fuses with that of the egg and completes the fecundation. 



The Embryo 



The egg may form a single embryo (Taxus, Sequoia), or each egg gives rise 

 to a group of four embryos (Pinus, Abies). The formation of the division-walls 



