AND AFFINITIES OF STEPHANOSPERMUM. 369 
are appended. PI. 42. fig. 8, from the upper part of the prothallial region, is from a 
seetion slightly tangential in plane. Above, it shows the tracheides in the nucellar wall 
(¢r.); below, where the macrospore-wall (m.w.) curves away to form the floor of the 
pollen-chamber, we see the greater portion of the tracheides lying against the nucellar 
wall (£r.!), a thin layer only remaining against the macrospore (£r.?). P1. 41. fig. 9, on the 
other hand, is a completely tangential section taken at the junction of the prothallial and 
pollen-chamber regions. Its plane is that running obliquely down from a, fig. 10. At 
the bottom of the figure 9 the macrospore-wall is seen cut through (m.w.) Rising up 
above this for a distance of some 15 mm. (in the figure) a compact sheet of almost parallel 
tracheides is seen. Here they are emerging into the lower region of the pollen-chamber 
(supra-arehegonial gap). The blank in the middle of the photograph is due to the fact 
that the tracheides run in a convex plane and consequently emerge from that of the 
section. On the flanks, however, the tracheides can be traced with little interruption till 
they disappear under the arching side of the pollen-chamber. The tattered cells (ep.) 
along the top and sides are the epidermal cells of this part of the pollen-chamber. 
The Pollen-chamber.—We now pass on to speak more particularly of the Pollen- 
chamber. ‘This term is rather loosely applied to the dome-shaped space occupying the 
distal extremity of the nucellus. In atypical case with fair preservation—as, for instance, 
that illustrated in Pl. 41. fig.2—immediately upon the horizontally stretching upper portion 
of the maerospore-wall (m.w.) is a broad space contained laterally by the thin nucellar 
wall and tapering to an angle which lies just above the sudden curve of the macrospore- 
wall. Above, it is roofed over in part by a septum, of which the middle parts are 
wanting (s.) Through the broad opening where the septum is incomplete the lower 
space communicates with another space which occupies the apex of the nucellus. 
This upper chamber is the pollen-chamber, and it is here that the pollen is found; the 
lower chamber (s.a.g.), whose form approximates to that of a frustum of a sphere, is empty, 
except that the floor and sides are littered with tracheides with spiral thickenings. The 
distribution of these tracheides and their relative abundance vary from specimen to 
specimen. Sometimes the sloping sides of the space are plastered with them as in 
fig. 11, whilst on the floor there is but a sparse scattering of tracheal fragments and 
drawn-out spirals; or the reverse may be the case; or, finally, approximately equal 
shares may occur on floor and sides. In no case, however, do the tracheides extend 
beyond the septum. The tapering corners of the space are generally loosely filled with 
mutilated trachcides (Pl. 42. fig. 12, /7.), the actual angle of the space tapering down into 
that zone of the nucellar wall which is occupied by the tracheal mantle. The obvious 
inference to be drawn from the foregoing is that the space did not exist at all in the 
earlier stages of development in the living seed, and that it has been produced by the 
withdrawal or contraction of the top of the macrospore from the septum (or true floor of 
the pollen-chamber). The top. of the macrospore was, no doubt, at an earlier stage over- 
laid with a tracheal covering which was merely a part of its general tracheal sheath or 
mantle (shown in the restoration, p. 372). It is the tracheal covering in this region 
that has become split, and the space merits the name of schizotracheal gap. The 
form and curvature and the occasional rupture of the macrospore-wall here are in 
SECOND SERIES.—BOTANY, VOL. VI. dn 
