24 Humphrey . — The Development of the 
they become much less so. As in other plants, they are 
closely packed with starch in the mature seed. Even before 
fertilization the cells of the micropylar part of the nucellar 
epidermis begin to elongate radially, so that a thick pad is 
formed at this point, through which the pollen-tube must 
penetrate ( m.p ., Fig. 45 ). Such a pad may be seen in the 
Marantaceae, but less markedly developed than here. It 
continues to thicken for some time after fertilization (m.p., 
Fig. 46), but finally becomes much compressed by the growth 
of the embryo, though still recognizable in the ripe seed 
(m.p., Fig. 48). After fertilization the embryo-sac enlarges 
at first far more rapidly at the base than at the apex (Fig. 46), 
but finally broadens above also to the full width determined 
for it by the micropylar collar (Fig. 48). Within this cavity 
the almost cylindrical embryo is formed, showing evident 
rudiments of two or more leaves of the plumule and of 
accessory roots (< emb ., Fig. 48). As in Canna , there is no 
suspensor. Unlike that of the previously described families, 
the endosperm of Costus and of other Zingiberaceae, perhaps 
of all, reaches a considerable thickness, although it never 
wholly fills the cavity. In the ripe seed of Costus it forms 
a single cell-layer over the micropylar end, and a layer 
several cells thick upon the wall of that part of the sac below 
the edge of the micropylar collar, more or less completely 
filling the space between the embryo and the wall of the 
cavity. As Tschirch (’£0) has remarked, the cells of this 
permanent endosperm contain no starch, but aleurone. So 
that we have here, instead of the single aleurone-layer of 
Canna , an aleurone-mass. But this fact need not modify 
our view of its role in the economy of the seed. 
In comparing members of other available genera of this 
family with Costus , several interesting points of difference are 
worthy of note. In the differentiation of the chief layer of 
the testa from the inner layer of the outer integument, in the 
presence of the micropylar collar and germinal lid, and in 
the development of embryo and endosperm, all the forms 
examined agree closely. In Donacodes elongata , Teijsm. et 
