174 BOTANICAL GAZETTE [MARCH 
A cross-section of the mature seed always shows a definite and deep 
constriction of the endosperm in the center, exactly opposite the two 
opposed vascular strands that run up on each side of the seed through 
the inner part of the outer integument (jig. 4). This constriction is 
the cross-section of two opposite and deep longitudinal furrows in the 
endosperm, and it means that in this longitudinal plane the endosperm 
encounters the greatest resistance in invading the perisperm. This 
most resistant perisperm certainly seems to hold a very definite topo- 
graphical relation to the principal vascular strands, and this relation 
may explain the resistance. 
_ That endosperm is the aggressive tissue at every point, even at 
.the region of most resistant perisperm, is evident for several reasons. 
In no case were the peripheral cells of the endosperm broken down; 
and in no case did there fail to appear one or two layers of disorgan- 
ized cells of the perisperm in contact with the endosperm (jigs. 30 
and 3r). In every case, also, the peripheral cells of the endosperm 
appeared active and very vigorous, and their different appearance in 
regions of more and less active encroachment is striking. In regions 
of active invasion the endosperm cells are radially elongated, and 
many of them are binucleate (jig. 30); while in regions of less active 
invasion the cells are more nearly isodiametric and rarely binucleate 
(fig. 31). 
Another proof that endosperm is the encroaching tissue may be 
obtained from comparative measurements. At the times of fertili- 
zation the gametophyte usually measures 20 by 30#. In the mature 
seed the ordinary length of the gametophyte is 20™™, the greatest 
width being 14™™, and the least (at the deep constriction opposite 
the vascular strands)) 1.5™™. At this most resistant region of the 
perisperm, therefore, where it is hard to escape the conviction that 
the perisperm plate has cut the endosperm nearly in two, the endo- 
sperm has increased its diameter against the perisperm seventy-five 
times. 
The best reason, however, for concluding that the endosperm . 
the invading tissue in this case is that this is always the behavior of 
endosperm; and it is singular that the old explanation of “ rumination’ ; 
was ever suggested. An examination of the nutmeg, the classic 
illustration of “ruminated endosperm,” and of Asimina triloba, 
