CHAPTER VIII 



THE EMBRYO AND SEEDLING 



THE EMBRYO 



The fertilized egg is the first cell of the sporophyte 

 generation. The earher stages in the development of 

 the sporophyte, while it is still within the seed, are 

 generally referred to as the embryo; subsequent stages, 

 as the embryo breaks through the seed coats and becomes 

 established in the soil, constitute the seedhng; later the 

 seedhng is called the plant. Attempts to apply these 

 terms too strictly are like applying the terms baby, child, 

 boy, and man. We know what is meant, but the process 

 is continuous, and attempts to make a strict definition 

 of embryo, seedling, and adult must be arbitrary, Kke 

 making the age of twenty-one years the dividing line 

 between the boy and the man. 



As the nucleus formed by the union of the egg and ^ 

 sperm nuclei enters upon the first division it is sur- 

 rounded by a great display of fibrous protoplasmic 

 structures contrasting sharply with the granular con- 

 tents of the rest of the fertilized egg (Fig. 62). It is 

 not at all surprising that a nuclear figure so small in 

 proportion to the mass of protoplasm fails to di\'ide the 

 fertilized egg into two cells. No wall is formed between 

 the two nuclei resulting from this first division, but the 

 two nuclei divide simultaneously; the four resulting 

 nuclei again divide simultaneously, and such free nuclear 

 divisions continue without the formation of any cell * 



