443 



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 



Ophioglossuni vulgafum, L. A = median-radial section through a very young spike 

 showing an initial cell (.r). 5= similar section of an older spike. C = transverse section 

 of a leaf, as along a line (/>) in A, traversing the young spike. Ophioglossum reticle 

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

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

 projecting spike, f, G = trans verse sections from the apex of a young spike of O. vul- 

 gatuiii, 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 B, 

 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 



