THE ACORN AND ITS GERMINATION. 15 



large cotyledons, without tearing them away from the 

 structures just described, he will find that each is at- 

 tached 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 

 fit 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 

 inclosing 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 en- 

 tirely of polygonal chambers or cells, with very thin 

 membranous walls, and densely filled with certain gran- 

 ule-like contents. These polygonal cells have not their 



