146 
WALTER P. THOMPSON 
and nourish some of the pollen tubes, and has a particular tissue 
developed for this purpose. This is a fact which must be given much 
weight in regard to the morphology of the envelopes of the female 
flower. At first sight it offers strong support to the contention that 
the inner envelope is really an ovary homologous to that of Angio- 
sperms. 
Moreover the fact that the pollen grains may germinate at a 
distance from the nucellus is a point which in itself closely connects 
Gnetum with the Angiosperms and removes it from the Gymnosperms. 
As stated by Coulter and Chamberlain (8) ''the chief contrast in the 
sporophyte is that in Gymnosperms pollination results in bringing 
the pollen grains in contact with the ovule while in Angiosperms the 
result of pollination places the pollen in contact with a receptive 
surface developed by the carpel." Whatever be the morphology of 
the inner envelope the essential point is that some of the pollen grains 
do not germinate on the nucellus as in Gymnosperms but at a distance 
from it as in Angiosperms. And by many botanists this is considered 
the chief contrast between the sporophyte of Gymnosperms and that 
of Angiosperms. 
That part of the inner integument surrounding the nucellus re- 
mains thin and undifferentiated. At the maturity of the seed it 
forms a thin, more or less papery covering of the endosperm. The 
middle envelope becomes differentiated into two tissues, an inner 
hard, stony layer, and an outer thin papery one, closely investing the 
stony layer and containing many sharp spicular cells. This outer 
layer of the middle envelope is quite thick at the top of the endosperm. 
The outer envelope becomes very thick. Its tip is papillate. It 
contains many resin passages and star-shaped spicular cells. At 
the maturity of the seed it forms a thick, fleshy, edible layer of a 
bright red color. 
Concerning the morphology of these envelopes there have been 
many opinions which may be summarized as follows: (i) All three 
are integuments resulting from the differentiation of the single in- 
tegument of Gymnosperms (Strasburger, 25) ; (2) the two innermost 
ones are integuments and the outermost is a perianth (Beccari, 3) 
or something analogous to it (Coulter, 7) ; (3) the two innermost ones 
are integuments and the outermost is an ovary or something analogous 
to it (van Tieghem, 32) ; (4) the innermost one is a true Angiospermous 
ovary and the outer two perianth or something analogous to it (Lignier 
