of the Endosperm during Germination. 449 



cotyledon ; but as the cotyledon increases in size, the sphere of 

 action of the ferment gradually extends towards the periphery of 

 the seed until all the tissue has been attacked and the cotyledon 

 completely fills the whole of the space previously occupied by the 

 endosperm. 



The progress of the ferment action in the case of the germina- 

 tion of the seed of Tamus may be described as centrifugal with 

 reference to the embryo, since the ferment, which apparently 

 proceeds from the cotyledon, affects first those walls of the endo- 

 sperm cells which are in immediate contact with it, and, as the 

 cotyledon enlarges pari passu with the disorganization and absorp- 

 tion of the endosperm, progressively extends its sphere of action 

 into deeper layers. 



At any given stage of germination the ferment action is 

 practically confined to a narrow zone of endosperm tissue, some 

 three or four cells deep, immediately outside the cotyledon. 



The seed of Galium Tricome, which was chosen as another 

 example of a thick-walled seed for comparison with Tamus, offers 

 quite a different type of ferment action during germination. 



Certain points regarding the general anatomy of the seed may 

 first be described. The seeds of Galium Tricome, which are 

 closely invested by the dry pericarp, have, as is well known, the 

 form of hollow spheres, slightly flattened on the ventral side, and 

 on this side also, a pore is left wdiich opens into the internal cavity. 

 The curved embryo lies buried in the endosperm, with its radicle 

 directed towards the basal portion of the seed 1 (Fig. 11). 



The endosperm is composed of thick- walled cells whose con- 

 tents stain a deep brown colour with a solution of iodine in 

 potassium iodide. Besides protoplasm and nuclei the cells con- 

 tain aleurone grains, which, together with the cell walls, constitute 

 the principal reserve materials. The cells do not shew any very 

 definite shape or arrangement, though they tend to radiate 

 outwards from the embryo. The walls are of varying thicknesses 

 and are irregular in outline, and thus shallow pits occasionally 

 occur, more particularly in those parts of the endosperm remote 

 from the embryo. 



The thick and irregularly- pitted walls of the endosperm are 

 richly provided with connecting threads, which are usually 

 arranged in barrel-shaped groups, though scattered threads also 

 occur. The threads, which are often beautifully curved, shew 

 a well-marked median node. No distinction can be drawn between 

 the groups of threads which occupy the pit-closing membranes and 

 those which are found in the thick parts of the walls, for often the 

 pits are only on one side of the cell wall (Fig. 16 (y)). In such cases 



1 Lubbock, "On Seedlings," vol. n., figs. 439 — 441. Le Maout and Decaisne, 

 p. 483. Engler and Prantl, Pjianzen-famiUen, iv. 4, p. 150. 



