LIFE HISTORY OF PINUS 65 



more dense as the pollen-tube advances through the nucellus. 

 Strasburger ('92) describes them as coarsely granular ; but, with 

 a high power, the presence of a reticulum which is sometimes 

 coarse and interrupted can invariably be made out in well pre- 

 pared material. By the time that these nuclei have reached in 

 their downward course the central portion of the nucellar cap 

 they have usually become very dense in structure (figs. 115 and 

 116), and frequently stain intensely, though they may show at 

 this time a weak reaction to dyes. The reticula of the two 

 nuclei may present the same appearance, or they may differ as 

 in the figures referred to above. The nucleolus, if it be present 

 at this time, is usually obscured by the dense network. Arnold! 

 ('00) described the sperm-nuclei in Cephaloiaxus as being grad- 

 ually filled with metaplasm. I find no evidence of such a proc- 

 ess in the development of these nuclei in Pinus. 



Archoplasmic areas similar to those figured by Chamberlain 

 ('99) have been observed in connection with the sperm-nuclei, 

 but as such granular accumulations may occur at any point in 

 the cytoplasm of the sperm-cells no importance is attached to 

 them. 



When the pollen-tube reaches the egg-, its apex is abundantly 

 supplied with cytoplasm, in the upper part of which the tube- 

 nucleus lies. The sperm-cell is just above with the stalk-cell 

 still in contact with the lower portion of its cytoplasm (fig. 120, 

 plate XII). Still higher up the tube may contain many starch- 

 grains. There is never any doubt at this time as to the identity 

 of the stalk-cell and the tube-nucleus in the material which I 

 have studied. Yet Dixon ('94) states that they cannot be distin- 

 guished, and Coulter ('97) describes them as having lost their 

 original outline. 



As many as six pollen-tubes have been found making their 

 way through the same nucellus, but, as a rule, not more than 

 three pollen-tubes renew their growth during the second season, 

 and frequently only two penetrate to the endosperm. The 

 effect of the pollen-tubes upon the upper part of the nucellar 

 tissue is very marked. The cells in the immediate vicinity of 

 the branched pollen-tubes early lose their protoplasmic contents 

 and their walls become crushed and broken. Those cells more 



