CONIFERALES 335 



haccata only the larger sperm enters the egg, the smaller sperm and 

 both the stalk and tube nuclei remaining in the pollen tube. In 

 Taxus canadensis all four nuclei enter the egg. In Torreya taxifolia^^^ 

 only the larger sperm enters. In the Podocarpaceae all four, with 

 some of the prothalHal nuclei, enter, but all except the functional 

 sperm degenerate at the top of the egg. In the Araucariaceae both 

 sperms and some small nuclei enter the egg. It should be remem- 

 bered that the stalk, tube, and prothallial nuclei look alike at this 

 time. The sperm nuclei have become so large that they are easily 

 distinguishable from the rest, reaching a length of 150 microns in 

 Araucaria braziliensis. Ghose^"' claims that the pollen tube pene- 

 trates the egg. 



In Cephalotaxus drupacea and C.fortunei both sperms get into the 

 egg, but one remains at the top and disorganizes there. 



In the Taxodiaceae generally only one sperm gets into the egg, 

 but in Sciadopitys both get in. Here it should be noted that the 

 archegonia are scattered in Sciadopitys, while in the rest there is an 

 archegonium complex. 



In Juniperus usually only one sperm gets into the egg. It is large 

 in proportion to the diameter of the egg, and its wall is torn off and 

 remains at the top of the egg, while the nucleus, surrounded by 

 much of its cytoplasm, moves down to fuse with the egg nucleus. 

 When the second sperm enters it remains at the top of the egg, ap- 

 parently undisturbed, recalhng the condition in cycads, where even 

 the cihated band is not disturbed when a second sperm enters the 

 egg. The first sperm opens the way into the egg so that a second 

 sperm enters easily. 



With the sperm, more or less cytoplasm enters the egg, where it 

 remains at the top and mingles with the general cytoplasm. When 

 the sperm is a highly organized cell, the cell wall comes off soon 

 after the sperm enters the egg, and the nucleus, with most of its 

 surrounding cytoplasm, moves down and unites with the egg nu- 

 cleus. The cytoplasm of the sperm forms a dense sheath, surround- 

 ing the fusing nuclei. The sheath is particularly conspicuous in 

 Juniperus,'^^^' '''^' Thuja,^^'' Torreya,^^^ and Tetraclinis^^^ 



Whether the sheath carries any hereditary characters is doubtful 

 since, in most conifers, only the nucleus reaches the egg. 



