THE ACOltN AND ITS GERMINATION 15 



away from the structures just described, he will find that 

 each is attached by a minute stalk to a sort of ridge just 

 beneath the tiny plumule ; this ridge is sometimes termed 

 the collar. He will also see that the plumule and radicle 

 tit closely into a cavity formed by the two cotyledons, 

 and so do not interfere with the very close fitting of 

 their two flat faces. 



Summing up these essential features of the structure 

 of the ripe acorn and its contents, we find that the 

 fruit contains within its pericarp (which is a more or less 

 complex series of layers of which the outermost is hard) 

 the seed ; that this seed comprises a membranous testa 

 enclosing an embryo ; and that the embryo is composed 

 of two huge cotyledons, a minute radicle, and a still 

 more minute plumule ; and that the tip of the radicle 

 is turned towards the pointed end of the acorn, lying 

 just inside the membranes. 



Leaving the details of structure of the membranes 

 until a later period, when we trace their development 

 from the flower, I must devote some paragraphs to a 

 description of the minute anatomy and the contents of 

 the embryo as found in the ripe acorn, so that the 

 process of germination may be more intelligible. 



Thin sections of any portion of the embryo placed 

 under the microscope show that it consists almost 

 entirely of polygonal chambers or cells, with very thin 

 membranous walls, and densely filled with certain granule- 

 like contents. These polygonal cells have not their own 

 independent walls, but the wall which divides any two of 



