MODE OF GROWTH OF BALLIA CALLITRICHA. 215 
ledge of the remarkable structure of which I have been endeavouring to convey an idea, 
one soon encounters an appearance, at first а very puzzling one, which, especially when 
viewed under à low power of the microscope, is readily misleading. Prof. Wright was 
the first to suggest the true solution of the contradictory appearance alluded to. But 
before I try to deseribe this, it will be necessary to convey an idea of the external or 
lateral form of the joints of the stems and rachises. 
The cells of the “© stems” and of each principal and secondary rachis of Mr. Moseley's 
plant are about + to $ as broad as long, and of a figure which has somewhat the aspect 
of an elongate oval (Pl. XXVIII. fig. 3). When more closely studied, especially under а 
higher power, they are seen to be of a cylindrical form for about $ or 3 their length from 
the base, at which point they become narrowed upwards, but in such a manner that 
thence to the summit the outline on each side gradually assumes a somewhat sigmoid 
eurve, the inward flexure at the upper portion being greater and somewhat more arched 
than that at the lower. Іп other words, at the place where the nearly cylindrical lower 
portion of the cell ceases it becomes gradually contracted; the outline, however, 
does not form any angle, but is rounded off and is thence continuously curved inwards, 
then upwards for a time almost vertically, soon imperceptibly beginning to be unin- 
terruptedly, but more rapidly, curved inwards on each side to the summit. Тһе diameter 
of the cells at the summit is usually about 2, or sometimes less, or it may be, on the 
other hand, nearly 1 of that of the cylindrical portion. I have called the lower portion of 
the eells nearly cylindrical; but they are not absolutely so, as they generally seem to 
be very gently and gradually concave on the lateral margins, the concavity being deepest 
about halfway from the base to the point where they become narrowed upwards. On the 
whole they mostly appear to be very slightly dilated from the concave middle to that 
point; that is to say, the widest part of the joint, by some very slight degree, is that 
just before where they begin to be narrowed by thesides curving inwards. So much for 
the contour (be it always understood of the cells of the principal stems and rachises) 
presented in the ordinary view, so far as relates to their external (that is lateral) 
boundary. 
I say, the ordinary view presented; for the habit of this plant being repeatedly 
distichous, the principal stems, branches, rachises, and their pinne or ultimate terminal 
offshoots, all lie in pretty nearly a common plane; hence a portion detached, however 
small, almost necessarily comes to be viewed from one or other of its plane aspects. The 
description given above of the lateral contour applies, it will be of course understood, to 
the joints so viewed. 
Now when they are examined in that position, the lower end of each joint of the 
Principal stems and rachises seems to be of a more or less conical figure, and broadly 
and bluntly rounded at the extremity, and as if projecting downwards into the joint 
immediately below ; the upper portion of the latter necessarily introverted to receive it 
(Pl. XXVIII. figs. 3, 10, 11, 14, 16; Pl. XXIX. figs. 15, 18). Not only has the structure 
the appearance described, but (if we are viewing this alga under a higher power) a slight 
alteration of focus further shows the base of the joints as broadly rounded off at a higher 
level, and as if the apex of the joint immediately below it were in close apposition 
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