426 



FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS. 



indeed, serves as a mechanism for supplying the embryo with moisture from the 

 germinating bed. For its successful operation it is necessary that the seed should 

 be favourably situated upon the soil, in other words, that these portions of tissue 

 which conduct water to the embryo should be in contact with the damp earth. 

 Such a position is promoted by the fact that in cases of the kind under discussion 

 the seed is so formed and its centre of gravity so adjusted that in falling the hilar 

 scar generally comes to lie underneath. The tissue here is more or less porous and 

 provided with lacunae, so that water can be taken up and transmitted to the 



embryo. Not infrequently 



V^ \ / K ^^^x ^ consists of loose stellate 



\ *A f/ -NX cells, and water is absorbed 



sWL wl /^T\ from the environment as 



by a sponge and placed at 

 the service of the deeper- 

 lying regions of the seed, 

 especially the embryo. 



In those seeds, on the 

 other hand, in which water 

 is not absorbed at definite 

 spots but over the whole 

 surface, there exist scat- 

 tered over the surface be- 

 tween the thickened imper- 

 vious cells, which form the 

 greater portion of the in- 

 vestment, special strings of 

 cells or minute canals which 

 at the proper time are per- 

 meable and serve for the 

 taking up of water. Thus, 

 for instance, in the hard, 

 round, black seeds of the 

 Indian Shot (Canna), the 

 testa, consisting as it does 



of an outer layer of thick-walled palisade-cells with several layers of transversely- 

 stretched stony cells beneath, constitutes an exceedingly strong protection for the 

 embryo. But over the whole surface of the seed are distributed tiny depressions, 

 at the base of each of which a stomate opens. Each of these stomates leads into 

 a canal of minute proportions traversing the layers of the testa and adequate for 

 taking up water at germination. 



Intimately connected with the developing seeds is the structure in which they 

 are contained, and in which they were originally fertilized. This is known at the 

 time of fertilization as the pistil or ovary, and later, when the seeds are ripe, as the 



Fig. 321. i Branch of Mezereon (Daphne Mezereum) with berries. 2 Fruiting 

 branch of the Lime (Tilia) with downy hairs investing the nut-like fruits. 

 8 Longitudinal section through a fruit of the Lime. 1 and natural size. 

 3 magnified. 



