46 VEGETABLE ORGANS. 



ripe seeds, the spot at which the funiculus has been 

 attached is mostly perceptible in the form of a scar. 

 The slight prominence of the foramen can also often 

 be distiuguished, as in the seed of chickweed (PI. I. 

 fig. 51*) ; in the ripe seed the foramen is termed the 

 micropyle, and towards it the radicle of the embryo 

 is always directed. 



One of the cells of the nucleus near its apex then 

 enlarges, so as to form a sac, called the embryo-sac. 

 This is excessively thin and transparent (PL I. 

 figs. 45 b & 47) ; and in it, also at the end next the 

 foramen, one or more (in the chickweed one) smaller 

 cells are formed from the cell-contents of the em- 

 bryo-sac, which are called the embryonal vesicles 

 (PL I. fig. 45 a). 



Thus far developed, the embryo exists prior to the 

 expansion of the flower and the discharge of the 

 pollen. The embryo -sac is not figured in this early 

 condition, the embryonal vesicle being then smaller 

 than that in fig. 45 b, although occupying the same 

 position. 



When the pollen has escaped from the anthers and 

 fallen upon the stigma, the pollen-tubes growing 

 down the intercellular passages of the style, enter the 

 foramen of the ovule, and so reach the apex of the 

 nucleus, at which the embryonal vesicle contained in 

 the embryo-sac is situated. The end of the pollen- 

 tube then adheres to the embryonal vesicle, and such 

 interchange of cell-contents takes place between them 

 as effects fertilization. 



The process of cell-formation in the fertilized em- 

 bryonal vesicle then takes place rapidly, new cells 

 being formed by the division of its cell- contents 

 (PL I. fig. 45 a) ; and it will be noticed that the new 

 cells are formed at the end of the embryonal vesicle, 

 opposite to that situated at the apex of the embryo- 

 sac. As the cell- division and formation proceed fur- 

 ther, a mass of new cells is produced (PL I. figs. 46 c 



