1910] BRIEFER ARTICLES 53 
large mucilage ducts, cells containing calcium oxalate, and epidermal cells 
containing tannin. The mucilage ducts begin development like sporangia, 
and for some time look like the functioning sporogenous tissue in the lower 
part of the sporophyll. Several hypodermal cells are differentiated from 
the rest by their greater size and their more vacuolate contents (jig. 6). 
Each of the cells divides into an outer and an inner cell, suggesting the pri- 
mary wall cell and primary sporogenous cell of the cycads (fig. 7). The 
inner cells by further division produce a mass of deeply staining tissue 
beneath several layers of cells with scanty cytoplasm formed by the division 
of the outer cells (fig. 8). As soon as this stage is reached the walls of the 
central mass of cells begin to disintegrate, probably by becoming mucilagi- 
nous (fig. 9), as soon the nuclei appear to be floating in a cavity filled with 
mucilage. Then the nuclei also disintegrate, and some of them with the 
remains of their surrounding cytoplasm are flattened against the wall of 
the widening cavity, forming a tapetum-like layer (fig. ro). Finally the 
whole central mass is replaced by a mucilage cavity. 
Discussion of the nature of the hump 
The sporophylls of Ginkgo resemble those of Taxus and Torreya. 
Taxus has a group of sporangia, five or more in number, surrounding a 
central axis. Torreya has four sporangia on one side of the axis, but in the 
primary Sporogenous cell stage seven sporangia appear; three of these dis- 
organize, being replaced by a single large resin cavity, leaving only four to 
come to maturity. Ginkgo has two sporophylls on one side of the axis, sur- 
mounted by the conspicuous hump containing mucilage ducts. The devel- 
°pment of the mucilage ducts from what appear to be abortive sporangia 
seems to indicate that the microsporophylls of Ginkgo may have come from 
a peltate type like that of Taxus. The fact that the sporophylls of living 
Ginkgo sometimes, and of fossil Ginkgoales as Baiera regularly, bear more 
than two microsporangia is additional evidence in favor of this view. 
The case would be quite clear if evidence could stop with the hump, 
but in examining the mucilage ducts in the leaves, I find that they also at 
first look like sporogenous tissue (fig. rr). So there are three lines of 
development that resemble one another: the functioning sporogenous tissue, 
the mucilage ducts in the hump of the sporophyll, and the mucilage ducts 
in the leaves; all have the same early history, starting with one or more 
cells which divide periclinally into outer and inner cells, the inner by further 
division forming a deeply staining mass, the outer forming several layers 
of wall cells. The tissue formed in the functioning sporangium we know is 
‘Porogenous as it later produces spores; the tissue in the hump of the sporo- 
