—60— 
of intercellular spaces. Fig. 8 illustrates a portion of a vertical sec- 
tion of a plant collected on July 10, which shows three somewhat 
clearly marked regions. There is an outer layer of epidermal cells, 
longer and narrower and more compact than the layers of chlorophyll- 
bearing cells below, which are bordered underneath by a double row 
of epidermal cells, from the lower of which the rhizoids develop. 
All the plants are provided with a thick mat of rhizoids which cling 
so tightly to the soil as to make it a very difficult matter to remove 
the particles of earth thoroughly enough for the safe cutting of ma- 
terial imbedded in paraffine. 
Pellia epiphylla is monoecious, the archegonia being formed in 
groups just back of the growing point and the papilla-like antheridia 
being borne on the upper surface of the thallus, more abundantly 
close to the midrib and toward the growing point, where they seem to 
slant a little forward in that direction. Their number is very variable 
as can be seen from the photograph in PI. VII. These antheridia ap- 
pear very early in the life of the plant, oftentimes being found in 
abundance on the tiny new thalli that spring out at the edges of the 
old plants, shortly after the spores are shed in the middle of April, 
and these antheridial dots persist throughout the life of the plant, being 
plainly seen even after the thallus has become brown in color and 
has begun to die down and disintegrate. 
The archegonia are formed in groups of varying numbers and are 
borne on the upper surface of the thallus just behind the growing 
point (Figs. 25. 26, 27b, 30*). They do not terminate its growth but 
usually after the appearance of the archegonia the forking of the costa 
begins at this point and two new divisions of the thallus develop more 
or less equally on either side, while the fertilized archegonium left at 
this point of division develops Into a sporogonium (Figs. 4e, 4f). 
Archegonia may again appear just back of the tips of these new 
branches. As soon as the archegonia are formed a layer of tissue 
grows^ out above and below (Figs. 26, 27a, 27b). The upper protect- 
ive layer, called the involucre, grows forward horizontally until it 
1. The development of the archegonium is described in “The Structure and De- 
velopment of Mosses and Ferns,” by D. H. Campbell, Ph. D. , as follows: 
“After the archegonium mother cell is cut off it does not at once divide by ver- 
tical walls, but there is first cut off a pedicel, after which the upper cell undergoes 
the usual divisions. ” “The archegonium mother cell * * * {§ divided 
by a transverse wall into a basal cell and an outer one from w'hich the archegonium 
itself develops. The divisions in this outer cell are remarkably uniform. Three 
vertical w^alls are first formed intersecting so as to enclose a central cell. In this cen- 
tral cell a transverse wall next cuts off a smaller, upper cell (cover cell), from a lower 
one. Subsequently the three (or in the Jungermanniaceae usually but two) first 
formed peripheral cells divide again vertically and by transverse walls in all of the 
peripheral cells, and somewTat later, in the central one. Also, the young archego- 
nium is divided into two tiers, a lower one or venter and an upper one, the neck. 
The middle cell of the axial row, by a series of transverse walls gives rise to the row 
of neck canal cells and the lowermost cell divides into two, an upper one, the ven- 
tral canal cell, and a lower one, the egg.” p. 16 & p. 90. 1895. 
*In Sept. no. 
