494 OPHIOGLOSSALES 
leaves were originally fertile. Abortion of the spike, partial or complete, 
accounts for its occasional absence, just as in Jsoe¢es. These two types, 
so similar in their embryology, are similar also-in the “ Se/ago” condition 
seen in their stunted stocks. The one, however, bears a simultaneous 
brush of leaves, the other, for reasons biologically intelligible, tends to the 
monophyllous habit: this difference is only one of time, not of form or 
of relation, and accordingly both types are equally referable to a strobiloid 
origin, with enlargement of the leaf, and of the spore-producing part which 
it bears. 
As regards factors of increase or decrease in number of sporangia, 
there may be some difference of opinion according to the view taken of 
the family as a whole. In accordance with the conclusion that the 
spore-producing spike illustrates an upgrade of development, there would 
be recognised as factors of increase, septation with continued apical 
growth of the spike, its branching and occasional fission: and in the case 
of Helminthostachys a further disintegration of sporangia and enation of 
sporangiophores. But there is no interpolation of sporangia so common 
a factor in Ferns. As factors of decrease there appear abortion of the 
whole spike, abortion of sporangia at the apex, and sometimes also at 
points lower on the spike, while a factor to be considered in addition is. 
the reduction down to one in number of leaves simultaneously expanded. 
The factors of increase may in this case be held to have successfully 
counterbalanced those of decrease, and the net result is a spore-output 
that appears numerically to meet the requirements of the plants, though 
their ultimate success in propagation is limited by the exacting conditions 
necessary for their germination. 
