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 ari< 

 constituting when mature the continuous, linear series of them seen in th< 

 drawings of the mature spike. But they are not always regular, an< 

 exceptions may be seen where the sporangia are imperfectly partitiom 

 or of anomalous outline. This is not surprising in bodies so nearly relat 

 to one another from the first. 



The two series of superficial cells composing the sporangiogenic ban< 

 soon divide periclinally, as well as in other directions, and form a broac 



FIG. 246. 



Ophioglossum vulgatum, L. A = median-radial section through a very young spike 

 showing an initial cell (x). B = similar section of an older spike. C~ transverse section 

 of a leaf, as along a line (tr) in A, traversing the young spike. Ophioglossum reticu- 

 laturn, L. D = tangential section of leaf (/) traversing the young rudiment of a fertile 

 spike. E another section from the same series, including the outer surface of the 

 projecting spike. F, G = transverse sections from the apex of a young spike of O. vul- 

 gatum, showing a construction with four initials. All Figs. X 100. 



and deep tract of tissue from which the sporangia are differentiated. Ii 

 position and origin they compare with those superficial cells which ii 

 other Pteridophytes give rise to the essentials of the sporangia. The 

 differentiation shows various successive steps leading to the final definitior 

 of those cells which are to form the spores. It will be readi< 

 understood from the structure seen in the large spike of O. pendulum 

 (Figs. 248, 249). Here certain cell-groups derived from the inn< 

 products of the sporangiogenic band soon begin to show more den< 

 protoplasmic contents : these are recognised as sporogenous groups, am 

 are seen in transverse section in Fig. 248 A, in radial section in Fig. 248 

 and in tangential section in Fig. 248 c. The result is that the inne 

 product of the band is segregated into alternate blocks of sterile an< 



