372 Bower . — The comparative examination of the 
characters as the details of meristematic structure as a ground 
for phylogenetic argument with respect to the series of Ferns. 
We see then that on comparing a series of forms which on 
independent grounds marks itself off, and ranges itself in 
order as a natural series, there is in every one of the meristems 
of the plant to be recognised a progression, as we pass along 
the series, from the simpler to the more complex, from a 
definite type of meristem, characteristic of lower organised 
plants, such as Bryophyta and Algae, to a less definite and 
more complex type characteristic of higher organisation, such 
as that of the Gymnosperms and Angiosperms. It may with 
confidence be stated that at no point in the vegetable king- 
dom is such a transition so clear and so marked as in the 
Ferns. The significance of this transition is not far to seek : 
the lowest terms of our series, the Hymenophyllaceae, have 
probably a joint alliance to the Algae and Bryophyta, and 
are plants of characteristically semi-aquatic habit, living for 
the most part in air saturated with moisture, and in accord- 
ance with this habitat they have thin extended rhizomes, 
membranous fronds, thin roots, projecting sporangia, and a 
delicate usually filamentous prothallus with antheridia and 
archegonia freely exposed : here is seen in every part a 
relatively great exposure of surface in proportion to bulk, and 
accordingly, were it not for the wetness of the habitat, there 
would be danger of drying up on exposure to the air. Pass- 
ing upwards along the series to the Marattiaceae, we see the 
transition by successive steps to plants capable of enduring 
without harm an exposure to considerable drought : we see, 
instead of the thin rhizome with scattered leaves, the thick 
upright stock with a terminal bud of leaves which protect its 
apex 1 ; instead of the membranous frond, the thick, almost 
coriaceous leaf with massive wings ; the roots instead of being 
thin become bulky : the sporangia do not project on a thin 
stalk, and so run the risk of drying up before maturity, but 
1 Here I speak in general terms : the majority (though not all) of the Hymeno- 
phyllaceae have creeping stems : the majority of the Marattiaceae have short, upright 
stems with crowded leaves ; but species of Danaea are exceptions to this. 
