1908] KILDAHL—PHYLLOCLADUS ALPINUS 341 



Hallii Burlingame (4) finds two prothallial cells, both of which 

 divide and form a tissue, consisting generally of six cells; a similar 

 condition was found in Dacrydium by Miss Young (16). Two more 

 divisions follow, so that the mature spore commonly contains four 

 free nuclei — prothallial, tube, stalk, and body nuclei. 



On November 1 the four-nucleate microspores are mostly found 

 lodged on top of the nuccllus (fig. 15) ; how much earlier they reach it 

 and how long they remain there is not known, as no material previous 

 to this date was available. In exceptional instances pollen tubes had 

 been formed and had penetrated the nucellus (fig. 18) ; but at this 

 date the tube contained only the four nuclei of the mature spore. On 

 December 11 the nucellus was in most cases entirely honeycombed 

 with pollen tubes, and very much disintegrated (fig. ig). The pollen 

 tubes do not pass deviously through the nucellus to any great extent, 

 nor branch, but pass almost in a straight line to the embryo sac. As 

 many as fifteen tubes were found in one ovule (fig. tq). 



Before the pollen tube enters the embryo sac the body cell divides 

 into two equal and optically similar male cells; it was impossible 

 to observe this division, but it takes place some time after the tube 

 has penetrated the nucellus and before it enters the embryo sac (figs. 

 20, jib). The entire contents of the pollen tube (five naked nuclei) 

 enter the egg (fig. 20). Arnoldi (i) also finds that in Cephalotaxus 

 the contents of the pollen tube are emptied into the embryo sac, the 

 contents in this case, however, consisting of only four nuclei; a similar 

 condition has been found in Pinus, where nearly the whole of the 

 contents of the tube is emptied into the cytoplasm of the egg (Coulter 

 and Chamberlain io, and Ferguson 12); according to Coker (8) 

 this may also take place in Taxodium (8) and in Podocarpus (7); 

 and Coulter and Land (9) report it for Torreya taxijolia. In 

 Cryptomeria Lawson (16) finds that only one male cell enters the 

 archegonium; and Jager (13) reports the same in Taxus baccata. 

 In Phyllocladus it is not uncommon to find the entire contents of 

 pollen tubes within the embryo sac after fertilization has taken place, 

 and even after the eight-nucleate proembryo stage (fig. 30); this is 

 no doubt due to the unusual open condition of the archegonia, the 

 greatly disintegrated nucellus (which seems to be of a very muci- 

 laginous consistency), and the large number of pollen tubes. 



