Miyake, The development of the gametophytes etc. 9 



tissue in Taxodium as not sporog'enous in nature, but as formed 

 from the niicellar cells siirroiinding' the megaspore mother-cell. 

 Miss Ferguson (1904) shares the same view in regard to the 

 tapetum in Pinus, and attributes to the tissue the function of 

 nourishing and protecting the growing prothallium. I have also 

 observed that the similar tissue in Ouniiinghamia originates from 

 undifferentiated cells of nucellus immediately surrounding the mega- 

 spore mother-cell, and am inclined to accept the latter Inter- 

 pretation. 



The growth of the young prothallium is very slow during 

 the first month of its development. Fig. 45 shows the stage 

 reached on April 30, and on May 17 it has reached the stage 

 shown in fig. 49. Growth then becomes more rapid and at the 

 beginning of June, the prothallium which is still only a protoplasmic 

 sac with an enormous vacuole surrounded by a cytoplasmic layer 

 containing numerous free nuclei, attains to a considerable size 

 (figs. 50, 109). Fig. 51 shows a part of the parietal layer of pror 

 toplasm in Hg. 50 more highly magnifled. Fig. 52 shows the 

 surface view of the same. The free nuclear division now ceases 

 and walls are developed bet^^'een the nuclei. The manner of the 

 wall-formation is shown in figs. 53—55. It seems to occur about 

 between June 10 and 15. 



The development of the prothallial tissue in Gymnosperms 

 was first carefully investigated by Mlle. Sokolowa (1890) and her 

 observations have, in general, been confirmed by most of the later 

 investigators. The early stages of the prothallium -formation in 

 Cunninghamia agrees on the whole with that described by Mlle. 

 Sokolowa. No wall is formed on the inner side of the protoplasm 

 facing the vacuole as first observed by Mlle. Sokolowa in other 

 Conifers. A section, made parallel to the inner surface of the 

 parietal layer of protoplasm, is shown in fig. 55. The cells are 

 polygonal in outline and contain some starch-grains. 



According to Mlle. Sokolowa, the first prothallial cells grow 

 inward forming long open tubes which extend to the center without 

 division; walls are then formed as the inner end of the tubes meet, 

 and later on the cells beconie divided by cross- walls. A similar 

 process of prothallium-formation was described by Arnoldi (1900) 

 in Seqnoia and the same was found to be the case with Taxodiiim 

 studied by Coker (1903). Noren's (1907) observations on Jimi- 

 'perus communis agree on the whole with those of Mlle. Sokolowa. 



Miss Ferguson'« description (1904) of the prothallium-for- 

 mation of Pinus differs somewhat from those of the above mentioned 

 writers. She states that "no cell has ever been observed to extend 

 from the circumference to the center of the prothallial cavity", and 

 the first prothallial cells are divided by cross-walls before they 

 reach the center of the vacuole. Lawson (1904 b) has observed 

 a similar thing in the early stages of the prothallium-formation of 

 Cryptomeria, although his Statement of the later stages differs 

 markedly from that given by any former investigators. My own 

 observations on the formation of the prothallial tissue in Cunning- 



