296 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
(one male and the other female), while the other bore a single short (female) 
lateral branch. In another instance a long branch bore a male receptacle, a 
short apical innovation (also male), and 5 short lateral branches (4 female 
and 1 male), These examples will give some idea of the variability encountered. 
In its histological features the thalius shows a delicate epidermis with 
slightly thickened walls and sometimes with minute trigones, the celis with 
oil bodies being few and scattered. The pores have a broad membrane around 
the opening and each is usually surrounded by 6 to 8 radiating series of cells 
with 8 or 4 (rarely only 2) cells in each series. The writer has not yet ob- 
served 5 cells, although Stephani gives this number as characteristic of A. 
austint. The green tissue shows much uniformity, although its thickness may 
vary from 0.15 mm. to 0.8 mm. in different specimens. The crowded supple- 
mentary partitions in the dorsal chambers often give the effect of filaments, in 
cross sections of the thallus, especially beneath the pores, where they fail to 
reach the epidermis. The compact tissue, composed of cells with numerous 
minute pits in the walls, occupies a strand, plane or slightly convex above; in 
the latter case the green tissue is a little thicker over the sides of the strand 
than over the middle, and the more deeply situated air chambers in this region 
are distinctly larger than elsewhere. Mycorhiza seems to be almost invari- 
ably present. The cells containing the hyphae tend to form a definite strand 
in the compact tissue, elliptical in section and variable in size. Their walls 
may be quite colorless but are usually purple, even in plants which are other- 
wise colorless. They are distinctly thinner than the walls of the cells with- 
out hyphae. 
The ventral scales never extend beyond the margins, except in the apical 
region, but show great variation in size and in extent of pigmentation. Fach 
scale contracts gradually into 1 or 2 appendages without showing a sharp line 
of demarcation. In the basal portion the marginal cells are slightly smaller 
than the median cells, and the slime papillae are usually short-lived and in- 
conspicuous, especially on deeply pigmented scales. The appendages are long- 
subulate or lanceolate, running out into slender cuspidate or filiform points. 
In most cases their margins are entire; they may, however, be vaguely crenu- 
late, and occasionally a marginal spine or cilium is present at the base (as 
Stephani described for A. wrightii). But even in plants where such spines 
occur they seem to be exceptional, many of the appendages being without them, 
so that they can not be considered of specific importance. 
The male receptacle is much more clearly defined than in the preceding 
species and is further distinguished by the fact that it always limits the growth 
of the male branch. It consists of a slightly elevated oval or circular disk, 
Sometimes with an apical notch, and is surrounded by a fringe of slender 
paleae which shrivel with age and are sometimes difficult to detect. The num- 
ber of antheridia varies but is usually rather large, and the ostioles are dis- 
tinctly elevated, especially on young receptacles. 
The peduncle of the female receptacle varies in length and the size of the 
disk also varies somewhat, according to the vigor of the plant and the num- 
ber of fertilized archegonia. The disk shows a central, strongly convex area 
and, in typical cases, 4 lobes extending obliquely downward and about as long 
as the diameter of the central area; sometimes the number of lobes is reduced 
to 8, 2, or even 1. The upper surface of the disk is covered over with coarse 
tubercles, each with an apical pore, these tubercles being especially prominent 
in the central area. The paleae of the peduncle are scattered except in the 
apical region and become much less conspicuous with age. The disk is usually 
green but sometimes shows a little purple pigmentation; the peduncle, on the 
