PYRONEMA. 113 
between the trichogyne and the antheridium, these nuclei collapse and 
break down into dense strands or shreds, which are frequently so 
connected as to form a coarse and much broken network in the cyto- 
plasm (Fig. 42,D). Thestructure of the mature sexual organs, which 
are aggregated in rosette-like clusters, is summarized by Harper as 
follows (1900, p. 344): 
The odgonium is a spherical or flask-shaped cell filled with dense protoplasm 
and many nuclei, which are very much larger than those of the ordinary vege- 
tative cells. Its stalk consists of two or three broad disk-shaped cells, of which 
the basal one is a part of the mass of thickened, swollen cells forming the base 
of the rosette. The apex of the odgonium is continued into the narrow conju- 
gating tube which curves upward to unite with the end of the antheridium. The 
antheridium is a curved, club-shaped cell, thickest near its upper end, and taper- 
ing gradually to its base, where it is continued into a stalk of one or more cells. 
The basal wall of the antheridium is, as a rule, somewhat higher up than that 
of the odgonium. It follows a somewhat oblique path upward, conforming 
rather closely to the surface of the odgonium, and its apex is even with, or 
reaches somewhat past, that of the latter. 
The mutual relation of the sexual organs will be best understood 
from Fig. 44. 
The changes taking place in the mature sexual apparatus, and which 
lead up to fecundation, are of much interest, especially when compared 
with the same process in other plants exhibiting similar phenomena. 
First among these are what may be termed the receptive spots of both 
the antheridium and the trichogyne. In that part of the antheridium 
near which the tip of the trichogyne presses against its wall and where 
the fusion-pore is formed, an area of protoplasm is differentiated as a 
finely granular and irregularly lens-shaped disk from which the nuclei 
have withdrawn. This granular area, although situated in the anthe- 
ridium, Harper very fittingly compares to the so-called mouth-piece, or 
receptive spot, of the egg in such alge as @dogonium and Vaucheria, 
The beak-like prolongation of the trichogyne reveals also a similar, 
though less conspicuous, cytoplasmic differentiation (Fig. 41, C; Fig. 
42, D). These areas seem to exercise a chemotactic influence which 
tends to bring together the tube and the antheridium, and also to secrete 
an enzyme by which the walls are dissolved in the formation of the 
conjugation-pore. The presence of a similar differentiation i in both 
the tube and the antheridium would seem to indicate also that the 
influence is mutual. 
At the point where the beak of the trichogyne is closely pressed 
against the antheridium the walls are dissolved and a pore is formed 
by which the cytoplasm of these two cells is made continuous (Fig. 
