448 OPHIOGLOSSALES 
spike, in the position ultimately to be occupied by the series of sporangia : 
it is derived from two regular rows of cells, which form part of the two 
abaxial quarters of the spike; but the usual regularity of their arrangement 
is liable to interruptions. It is from this band that the sporangia arise, 
constituting when mature the continuous, linear series of them seen in the 
drawings of the mature spike. But they are not always regular, and 
exceptions may be seen where the sporangia are imperfectly partitioned 
or of anomalous outline. This is not surprising in bodies so nearly related 
to one another from the first. 
The two series of superficial cells composing the sporangiogenic band 
soon divide periclinally, as well as in other directions, and form a broad 
Fic. 246. 
Ophioglossum vulgatiin, L. A=median-radial section through a very young spike 
showing an initial cell (x), &=similar section of an older spike. C=transverse section 
of a leaf, as along a line (¢~) in A, traversing the young spike. Ofphioglossum reticu- 
latum, L. D=tangential section of leaf (2) traversing the young rudiment of a fertile 
spike. A=another section from the same series, including the outer surface of the 
projecting spike. #7, G=transverse sections from the apex of a young spike of Q. wul- 
gatum, showing a construction with four initials. All Figs. x 100. 
and deep tract of tissue from which the sporangia are differentiated. In 
position and origin they compare with those superficial cells which in 
other Pteridophytes give rise to the essentials of the sporangia. The 
differentiation shows various successive steps leading to the final definition 
of those cells which are to form the spores. It will be readiest 
understood from the structure seen in the large spike of O. pendulum 
(Figs. 248, 249). Here certain cell-groups derived from the inner 
products of the sporangiogenic band soon begin to show more dense 
protoplasmic contents: these are recognised as sporogenous groups, and 
are seen in transverse section in Fig. 248 a, in radial section in Fig. 248 8, 
and in tangential section in Fig: 248 c. The result is that the inner 
product of the band is segregated into alternate blocks of sterile and 
