10 Miyake, The developmeiit of the gametophytes etc. 



hamia agree on the whole with the description of Miss Ferguson. 

 As the first prothallial cells elongate toward the center of the va- 

 cuole, they divide several times by cross walls before reaching- the 

 center of the cavity. A part of the prothallial tissue as they half 

 way advanced toward the center of the vacuole is shown in fig. 57. 



The filling up of the central vacuole with growing prothallial 

 tissue proceeds rather rapidly, and in about a week after the first 

 wall-formation the whole megasporic or embryo-sac is filled with 

 solid tissue. The stage just after the formation of the solid pro- 

 thallial tissue is shown in fig. 58. Arnoldi (1900), Coker (1903), 

 Lawson (1904) and several other recent investigators, confirming 

 an earlier Statement of Strasburger (1880), have noted many 

 nuclei in each of the young prothallial cells. Miss Ferguson 

 (1904), however, has "not observed multinucleated cells in 

 the prothallium of Pinus up to the time when the suspensor 

 has elongated and carried a several celled embryo to a considerable 

 depth into the endosperm." Sheadds: "There is often an appearance 

 of more than one nucleus in a cell, but careful study never falls 

 to demonstrate a delicate cell-wall between the nuclei. At an 

 early stage in prothallial development the cell-walls are very de- 

 licate, scarcely more than condensations of the ectoplasm so that 

 they might easily be mistaken, in Pinus, for Strands of cytoplasm. 

 Doubtless the cells become plurinucleated during a more advanced 

 stage in embryo formation." I have also failed to find multi- 

 nucleated cells in young prothallium of Cunninghmnia, but in the 

 older prothallium, some of the ceUs seemed to contain more than 

 one, usually two, nuclei in each. Careful study has sometimes 

 proved that some of those cells are only apparently bi- or multi- 

 nucleated, a very delicate wall being found between the nuclei. 

 Thus most of the cells of the mature prothallium were found to 

 be uninucleated. 



It was often maintained that the nuclear division in the pro- 

 thallium is sometimes amitotic. Mlle. Sokolowa (1890) makes 

 a similar Statement in her studies on the prothalliuni-formation 

 of various Gymnosperms. Noren (1907) nientions that "Diese 

 Teilung (division of the first prothallial cells) ist oft amitotisch, 

 was auch von Sokolowa erwähnt wird". Coker (1903), on the 

 other hand, states that "these nuclear divisions are generally, at 

 least, of the mitotic type". So far as my Observation goes, the 

 division takes place mitotically, and no case was come across in 

 which the nucleus showed a sign of amitosis. 



The w^all enclosing the female prothallium, or the megaspore- 

 membrane is at first thin and delicate. During the growth of the 

 prothallium the membrane bccomes thicker and more conspicuous. 

 Fig. 51 shows the female prothallium just ))efore the wall-formation 

 and the megaspore-membrane is found about half way thickened. 

 In figs. 53 and 54 the double nature of the membrane, as clearly 

 pointed out by Thomson (1905) in other Gymnosperms, is more 

 prominent. In the mature prothallium, the exosporiura shows 

 characteristic radial striations and is several times as thick as the 



