Embryo of Pseudolarix. 641 
on May 13, 1904, which were in the last stage of pollination, the latter had 
probably begun at the beginning of the same month. 
The further development of the male gametophyte after pollination 
has not been investigated. 
The Female Gametophyte. 
The division in the formation of the megaspores seems to occur about 
the time of pollination, the megaspore mother-cell being as a rule solitary 
in each ovule. Stages of the division were not observed, nor has the 
number of potential megaspores been determined. The lowest of the 
megaspores soon begins to enlarge and develops into the female prothal¬ 
lium, while the upper sister cells gradually disintegrate and are crowded 
to the upper corner of the growing gametophyte. Fig. 12 shows a young 
female gametophyte with two free nuclei which are embedded in the 
parietal layer of cytoplasm surrounding a large central vacuole, and the 
disorganizing remains of the sterile megaspores are seen at the upper part 
of it. It is probable that the parietal layer of cytoplasm is organized at 
one-nuclear stage, as has already been reported in Pinus (Ferguson ’ 04 ) and 
Cimninghamia (Miyake TO). The free nuclear division in the megasporic 
sac takes place hand in hand with the enlargement of the latter as in other 
Conifers. 
Fig. 13 shows the condition of a young female prothallium about four 
weeks after that of Fig. 12. It is surrounded by several layers of well- 
developed tapetal cells. After much enlargement and more nuclear divisions, 
the walls are formed between the nuclei, and finally the entire megasporic 
sac is filled up with compact prothallial tissue. At this time the tapetum 
is much compressed by the growing prothallium, and shows signs of dis¬ 
integration. 
The so-called megaspore membrane enclosing the female prothallium 
is at first thin and delicate. During the growth of the prothallium the mem¬ 
brane becomes thicker and more conspicuous. Its structure and thickness 
are on the whole similar to those described for other Abietineae (Thomson 
’ 05 , Lawson ’ 09 ). Fig. 14 is drawn from the lateral basal region of a mature 
prothallium, showing the well-developed megaspore membrane, which 
measures about 4-5 jll in thickness. The exosporium shows characteristic 
radial striations, and is several times as thick as the homogeneous endo- 
sporium. Thomson (’ 05 ), who has studied the megaspore membrane in 
five genera of the Abietineae, states that in this group ‘ the coat is thick in 
the chalazal region, and thins out gradually towards the micropylar portion 
of the prothallium, being not more than one-third as thick at the apex as 
at the base of the macrospore ’. He found, however, that in Larix c there is 
scarcely a trace of the megaspore coat in the archegonial region Lawson 
(’ 09 ) also found a similar thing in Pseudotsuga , and says that ‘ at a plane 
