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AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
variations indicate that Reboulia is a plastic form in the development of 
the antheridium. 
The divisions of the primary spermatogenous cells follow no regular 
plan (figs. 40, 45, 46), although their original boundaries can be detected 
for a considerable time in the development of the tissue (fig. 16), especially 
when division takes place, as all the offspring of a primary spermatogenous 
cell usually divide simultaneously. The wall is a single layer of cells and 
retains its form until the maturity of the sperms. The young antheridia 
are somewhat erect, but by the time of maturity have become strongly 
inclined (figs. 13, 16). 
The Morphological Nature of the Receptacle 
There have been two interpretations of the male receptacle of Reboulia. 
The one, first suggested by Hofmeister (18), regards it as a shoot; the other, 
put forth by Leitgeb (21, 22), holds it to be merely a dorsal outgrowth. 
This latter view is based on the claim that the apex of the thallus is not used up 
in its formation. Even if the thallus is permanently checked, the apex is 
thought to be evident below the disc. Leitgeb regards the lunate disc as 
merely a repetition of the form of the thallus notch. Cavers (6, 7), support- 
ing the former idea, says: 
The male receptacle of Reboulia may be regarded as representing a branch, having on 
its anterior margin a single growing point, or, in many cases, two growing points. Apart 
from the fact that the branching in the latter case takes place at a late stage, after several 
antheridia have been formed, and occurs once only, giving rise to a crescent-shaped recep- 
tacle, there is no essential difference between the receptacle of Reboulia and that of Fega- 
tella, in which the branching takes place at an earlier stage and is repeated several times, 
giving rise to radiating rows of antheridia. 
He holds the growing point to be used up in the formation of the recep- 
tacle, and in some cases to branch, giving the two horns of the disc. The 
continuation of the thallus in front of the receptacle is regarded as an inno- 
vation shoot. Goebel (14) from his study of Monoselenium tenerum, a 
monoecious form with the male receptacle behind the female, which latter 
may also become dorsally placed, finds that the sessile male disc may be 
elevated on a short stalk with scales and rhizoids, but without a rhizoid 
groove. Both receptacles in Monoselenium, according to Goebel, represent 
branch systems, the antheridia developing in centrifugal order on the upper 
surface. He regards the forward growth of the thallus as an adventitious 
branch. From Goebel's claim that the receptacle of a "branch-system" 
type may become dorsal Cavers (8) concludes that a 
Composite receptacle . . . need not necessarily terminate the growth of the thallus 
but may come to occupy the same position as the "dorsal outgrowth" type of receptacle 
which Leitgeb regarded as contrasting so strongly with the "branch-system" type. 
Goebel (14, 15) would explain the dorsal sessile receptacles, such as 
occur in Reboulia and Plagiochasma, as reduced from those of forms such as 
