288 PHYLUM XIV. ANTHOPHYTA 



finally takes the form of a very small stem, tipped with 

 a root at one end, and bearing two rudimentary leaves 

 at the other. In the meantime the immature game- 

 tophyte resumes its development as the result of the 

 union of the second sperm nucleus with the two polar 

 nuclei to form the so-called endosperm nucleus, which by 

 its rapid division, with much delayed formation of cell 

 walls, results in the development of a mass of tissue 

 surrounding and nourishing the embryo sporophyte 

 and filling the growing ovule. It is now known as the 

 endosperm, but it is in reality only the belated game- 

 tophyte. 



522. The ovule has now grown much in size. Ex- 

 ternally its outer coat has become thicker and harder, 

 while internally the gametophyte has enlarged and solidi- 

 fied. A layer of cells at the base of the ovule now 

 becomes corky and checks the supply of water, drying 

 and hardening the whole ovule, and stopping further 

 growth. In this final state the ovule is called the 

 seed. 



523. In the Buttercup the carpel enlarges to accom- 

 modate the growing ovule, but finally its tissues harden 

 and dry so that when the seed is mature it is contained 

 within the close-fitting wall of the old carpel and, in this 

 condition, it finally falls off from the flower axis and is 

 known as a fruit. The term "fruit," therefore, is here 

 used for the ripened carpel and its contained seed, and 

 in flowering plants this is the generally accepted signi- 

 fication of the term. 



524. When these fruits fall to the ground and absorb 

 moisture, the embryo plant in each seed renews its 

 growth, getting its food from the endosperm. At 

 length it is able to push out a root into the soil, and much 

 later it escapes wholly from seed and fruit and pushes up 



