LIFE HISTORY OF PINUS 1 13 



arise in its cytoplasm. At first these are irregularly scattered 

 throughout the cell, though more prominent at its periphery ; 

 in the mature egg, they are largely confined to the peripheral 

 portions of the lower half of the cytoplasm. It is suggested, 

 though not definitely demonstrated, that these nutritive spheres 

 are the products of nucleolar activity, having originated within 

 the nucleolus of the egg and the nucleoli of the sheath-cells. 



The egg-cytoplasm presents a delicate reticulum, in which, at 

 times, fibers occur. Immediately preceding fertilization, an 

 opening arises in this cytoplasm, just below or in the near 

 vicinity of the neck-cells. This cavity is apparently formed for 

 the reception of the sperm-cell, and the name " receptive 

 vacuole " has been applied to it by the writer. 



CHAPTER IV. 

 FERTILIZATION AND RELATED PHENOMENA. 



CONJUGATION. 



The Coming Together of the Gametofhytes. When the 

 time for fertilization arrives the pollen-tube has forced its way 

 between the neck-cells of the archegonium and stands just above 

 the egg (fig. 120, plate XII), but it does not under normal con- 

 ditions enter the archegonium. The fact that the pollen-tube in 

 Pinus does not penetrate the egg has recently been observed by 

 Blackman ('98), and Coulter and Chamberlain ('01). Standing 

 just above the egg, the apex of the tube is ruptured and almost 

 all of its contents passes into the cytoplasm of the egg. The 

 sperm-cell with its dense cytoplasm and two nuclei, the tube- 

 nucleus, the stalk-cell, a part of the cytoplasm from the pollen- 

 tube, and some of the starch grains from the male gametophyte 

 can all be distinctly recognized in the upper part of the oosphere 

 (figs. 212-215, plate XIX). Dixon ('94) noted the passage into 

 the oosphere of the four nuclei of the pollen-tube, but he could 

 not distinguish between these after their entrance into the egg. 

 Blackman confirmed Dixon's observations as to the passage of 

 these nuclei into the oosphere and believed that the cytoplasm 



