508 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
exterior of the macrospores of Selaginella Martensii. In my previous memoir (loc. 
cit., p. 347) I was unable to discover any evidence that smaller cells occupied the 
spaces, cl, intermediate between the hour-glass cells, hence I was disposed to believe 
that the constricted portions of those latter were surrounded by a crypt-like cavity, 
whose ramifications were co-extensive with the entire sphere. But on bringing one 
of the new oil-immersion lenses made by Kleiss, of Jena, to bear upon an oblique 
section I discovered that this was an error. 
Fig. 28 represents a portion of the section in question enlarged 320 diameters. At 
a we have the inner extremities of the cells forming the continuous boundary of the 
central cavity of the organism. At b are the constricted portions of the same cells rising 
up like a series of hollow pillars from their closely-united flattened bases. At c these 
cells again expand, and form by their conjunction a second or outer continuous tissue, 
whilst them constricted portions, b', now appear descending from them like so many 
funnels ; at d, d, we have some of these cells prolonged into hollow tapering hairs. But 
what is most significant in this section is the series of extremely delicate lines, e, which 
proceed from one constricted cell to its next neighbour, and which in several instances, 
as at e', are seen to be double. The discovery of these lines, which unquestionably repre¬ 
sent the two walls of extremely thin-walled, contiguous cells, demonstrates that the 
lozenge-shaped interspaces (cl, of fig. 24) are really occupied by a delicate parenchyma.* 
Fig. 25 is a section through a slightly crushed specimen exhibiting a transverse 
section of the sporocarpal wall at a, and a tangential one of the outer surface of the 
same wall at c. In the interior of the organism is a structureless membrane con¬ 
taining a small number of relatively large cells. I had already figured a similar 
membrane, but devoid of cells, contained in Plate 23, fig. 67, of my previous memoir, 
and also another in fig. 69a of the same Plate. In the latter case the membrane is 
filled with numerous small parenchymatous cells, varying from ‘001 to '0015 in 
diameter. In the specimen now described these cells are nearly double that size, 
the largest being ‘0025 in diameter. 
Figs. 26 and 27 represent two specimens intersected more tangentially. The former 
of these is especially important, because whilst it displays the peripheral ends of the 
* Since writing the above description I have discovered the specimen represented in fig. 57. It is a 
tangential section of the wall of the above fruit which displays the outer surface of the organism, where 
the cells, a, are arranged with great regularity and approximate uniformity of size. At b, b, we have 
the inner bases of four hams, which are merely outward prolongations of some of the cells, a. Opposite 
c the section has penetrated a little more deeply into the structure, bringing into view a lower, optical 
section of the tissues forming the centre of the fruit-wall. At d, d, we have optical sections of the con¬ 
stricted portions of the hour-glass cells, and at e, e, we have the radiating walls of five or six cells which 
surround these central constricted portions. These are here seen so distinctly as to place the existence 
of a central layer of smaller cells, occupying the lozenge-shaped space d of fig. 24, beyond all doubt. 
In fig. 57 it is the outer conjoined extremities of the hour-glass cells that'are in focus. The radiating 
walls of the central cells, d, are seen through and below the funnel-shaped contracting walls of the surface 
areolations under a low magnifier. 
