446' OPHIOGLOSSALES 



Helminthostachys. Such a difference is of common occurrence within near 

 limits of affinity. For reasons given in Chapter XVI. the upright radial 

 type will be held to be the primitive, and the dorsiventral as seen in 

 Helminthostachys the derivative : it is interesting to note that this goes 

 along with a large and heavy leaf-development. 



While, however, there may be no doubt of the homology of the spike 

 in all the three genera, it is to be noted that the level of its insertion 

 upon the adaxial face of the sterile leaf is not constant. In most species 

 of Ophioglossitm, as also in Helminthostachys, it is at the base of the 

 sterile lamina ; but in O. Bergianitm, where there is no differentiation of 

 petiole and lamina, it is but a short distance above the insertion of 

 the leaf itself upon the axis. In O. pahnatum it has been seen that the 

 numerous spikes may be distributed over a considerable length of the 

 basal region of the lamina. In Botrychiuin the differences in respect of level 

 of insertion are more marked : in B. Lunaria it is usually a short distance 

 below the lowest pair of pinnae : in B. ternat^lm it may be about four 

 inches below them, and about two inches from the base of the frond : 

 in B. daucifolium the insertion may be close to the base of the frond ; but 

 in B. virginianiim, on the other hand, it may be above the second pair of 

 sterile pinnae. The chief question in the morphology of the Ophio- 

 glossaceae will be as to the real nature of this member, which shows so 

 variable a level of insertion, though it maintains in a remarkable degree 

 its constancy of character, as well as its position upon the upper face of 

 the leaf. A knowledge of its development and internal structure will be 

 essential before arriving at any definite conclusion. 



Lastly, in comparing the shoot of the Ophioglossaceae as a whole 

 with that of the strobiloid types, the essential relation of leaf to axis is 

 the same. The nearest resemblance as regards general proportion is with 

 Isoetes, both having the stunted axis and spiral arrangement of the relatively- 

 large leaves : one main difference lies in the tendency to the monophyllous 

 habit in the Ophioglossaceae, which may be held to be a consequence of 

 its perennation underground. It has been seen that in Isoetes all the 

 leaves of the mature plant show evidence of being potentially fertile, but 

 that an early abortion of the sporangia leaves some of them sterile. A 

 similar abortion is seen in the Ophioglossaceae : in O. vitlgatum a rudi- 

 mentary spike is often to be seen on apparently sterile leaves, as a small 

 peg-like growth in the place where the normal spike would be inserted : 

 it is shown in Fig. 235 A, letter /. In other cases it may be found 

 that no vestige of the spike remains. Similar abortive spikes have been 

 seen in O. reticulatum and pendulum. In Botiychium Lunaria and simplex 

 extraordinarily small plants are found to bear fertile spikes, porportional 

 in size to the sterile lamina : but in some cases of small, weak plants 

 the fertile spike appears to be entirely absent. In Helminthostachys Lang 

 observed that abortive fertile spikes are commonly found, subtended in 

 each case by a fully developed sterile lamina. It thus appears that the 



