1906] CHAMBERLAIN—OVULE OF DIOON 341 
gametophyte is still spherical is cut through the middle, the gameto- 
phyte, as seen with the naked eye, has a beautiful, radiating appear- 
ance, looking somewhat like a transverse section of a twig with very 
fine and numerous medullary rays. Until late in December the endo- 
sperm is almost transparent, so that the young archegonia are easily 
seen and counted, even when the endosperm is removed entire. Ordi- 
nary newspaper print can be read through a section of endosperm 
4™™ in thickness. At this stage the endosperm tastes sweet on account 
of the abundant sugar, but as soon as starch begins to form it takes 
on a translucent white color, and as the starch becomes abundant an 
opaque white. Even before the starch begins to appear, the endo- 
sperm commences to elongate, and in February has reached a length 
of 15™™ and a breadth of 1o™™. In April, when the endosperm has 
reached its full size, it is about 25™™ in length and 17™™ in breadth. 
Early in December there not only is no archegonial chamber, but 
the top of the gametophyte containing the young archegonia is even 
elevated (fig. 15). In February the tissue at the rim of the elevation 
begins to grow rapidly, while the growth of the elevation itself is 
checked; consequently, the elevation soon becomes the bottom of the 
archegonial chamber ( jig. 16). At the time of fertilization the arche- 
gonial chamber has reached a depth of 1 to 1.5™™ (jig. 17). 
The megaspore membrane—Early in November, while the endo- 
sperm is still spherical, the megaspore membrane is well developed. 
In fresh material one might easily mistake the endosperm jacket for 
the membrane, but the jacket is much coarser and can be stripped off 
entire with forceps. The membrane is comparatively delicate, but 
pieces several millimeters in length may be stripped off with forceps. 
When the nucellus is removed, the portion of the membrane covering 
the archegonia usually adheres to the nucellus rather than to the endo- 
sperm. The membrane is thinner at the apex and base of the endo- 
sperm than on the sides. In young ovules, with the endosperm still 
spherical, the greatest thickness of the membrane which was measured 
Was 3m at the apex, 3.1m at the base, and 4.5 at the sides. The 
average at this stage is about 3 at the base and apex, and 4.14 at 
the sides. In ovules whose endosperm has reached a length of 1.5°™, 
but in which the archegonial chamber has not yet begun to form, the 
membrane is rather uniformly about 5 in thickness. In germinating 
