DIV. n 



SPERMATOPHYTA 



567 



Araucaria thus stands nearest to the Abietineae. In the Cupressineae two equal 

 generative cells are found throughout. Taxus has a single generative cell ; the 

 sister cell produced on the division of the antheridium mother cell is greatly 

 reduced. 



As a rule the macrosporophylls bear two macrosporangia. The 

 single mother cell undergoes a tetrad division (Fig. 544), and of the 



four resulting cells only one 

 develops into an embryo-sac 

 (macrospore). This, as it in- 

 creases in size, first crushes 

 its sister cells and later the 

 whole sporogenous complex of 

 cells. Meanwhile, by the re- 

 peated division of the nucleus 

 and protoplasm, the macro- 

 spore becomes filled with the 



Fio. 545. Median longitudinal section of an .ovule of 

 Picea excelsa at the period of fertilisation, e, Em- 

 bryo-sac filled with the prothalliura ; a, archegonium 

 showing ventral (a) and neck portion (c) ; o, egg-cell ; FIG. 546. Archegonium of Pinus laricio 

 n, nucleus of egg-cell ; nc, nucellus; p, pollen-grains ; 

 t, pollen-tube; i, integument; s, seed -wing, (x 9. 

 After STRASBUROER.) 



before the separation of the ventral- 

 canal-cell, (x 104. After COULTER and 

 CHAMBERLAIN.) 



tissue of the prothallium (Fig. 545). The archegonia are formed at 

 the apex of the prothallium ; each consists of a large ovum and a 

 short neck. As in the Pteridophytes a small ventral canal-cell is cut 

 off from the egg-cell shortly before fertilisation (Fig. 546). The 

 development of the embryo from the fertilised ovum presents great 

 differences in the several orders and even genera, and the following 

 description applies to the species of Pinus (Fig. 547 D-K). 



By two successive divisions of the nucleus four nuclei are formed 

 which pass to the base of the egg-cell, where they arrange themselves 



