422 



FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS. 



early, before the seed enters on its resting-stage. The ultimate fate of the food- 

 material is the same in both cases, i.e. to nourish the young plant. 



The relations of the embryo to its reserve-tissue are very various. In many 

 plants, e.g. Pimpernel, Wood Sorrel, Snapdragon, and Strawberry-tree (Anagallis, 

 Oxalis Acetosella, Antirrhinum m,ajus, Arbutus Unedo, cf. figs. 3173,4,5,6,7,8,9,10^^ 

 the straight embryo lies embedded in its reserve-tissue. The same relations obtain 

 in the Eue (Ruta graveolens, cf. figs. 317 ^ and 317 ^), the embryo here being slightly 

 bent; whilst in Phytolacca decandra (fig. 317 ^^), on the other hand, the embryo is 

 outside its reserve-tissue, and curved around it like a horse-shoe. In Sapindaceae 

 and Chenopodiaceae the embryo is spirally twisted. In the Grasses it is laterally 

 placed to its reserve-tissue (cf. vol. i. p. 599, figs. 141 ^ and 141 *), and the manner 

 in which it utilizes its reserve has been already fully described in vol. i. p. 604. 



Fig. 317. — Seeds with a Reserve-tissue. 



1 Ruta graveolens, the intact seed. 2 Longitudinal section of the same. » Oxalis Acetosella, intact seed. < Longitudinal 

 section of the same. ^ Anagallis phoenicea, intact seed. 6 Longitudinal section of the same. ' Arbutus Unedo, intact 

 seed. 8 Longitudinal section of the same. 9 Antirrhinum, majus, intact seed. 10 Longitudinal section of the same. 

 II Longitudinal section of seed of Phytolacca decandra. (After Baillon.) 



Both the embryo and its reserve-tissue increase at the expense of the tissue 

 immediately external to the embryo-sac; and in the ripe seed very slight traces of 

 this tissue are to be found. Only in relatively few seeds is food stored in this 

 peripheral tissue (i.e. in the tissue of the nucellus between the integument and 

 embryo-sac). Under these circumstances this nucellar tissue assumes very much 

 the character of the more usual reserve-tissue (endosperm) which is formed within 

 the embryo-sac. Its cells become filled with fat, starch, and proteids, which serve 

 later on as food-material for the young plant. Reserve-tissue when stored within 

 the embryo-sac is termed endosperm; this, which arises external to the embryo-sac 

 is, in contradistinction, termed perisperm. 



It is worthy of note that a formation of reserve-tissue does not take place in 

 ovules which are not fertilized. The act of fertilization obviously exerts an influence 

 not limited to the embryo. One may compare this influence to the impulse gene- 

 rated when a stone is thrown into still water. Just as waves travel in ever- 

 widening circles from the centre of disturbance, so it is with the changes in the ovule: 

 first, changes are noticeable in the egg-cell, then successively in the embryo-sac. 



