merisiems of Ferns as a Phylogenetic Study . 377 
the root is the first to depart from the simpler growth with 
a single initial, and even in Todea it appears to settle down 
into a definite type. The stem is the next to depart from the 
definite type of the simpler Ferns, while the apex of the leaf 
is most conservative in its characters, and even in Marattia , 
which shows greater complexity of apical construction both in 
root and stem, the leaf still shows, at least while young, a 
fairly regular segmentation from a single initial. This is, 
however, finally lost in Angiopteris . Thus there is not a 
strict parallelism of progression from the simpler to the more 
complex type of construction of the meristems, of a single 
species or individual, even within the series of plants specially 
examined. 
Turning to other members of the Vascular Cryptogams, 
further exceptions are to be found, such as the Ophioglossa- 
ceae 1 : these being members of the Filicineous series, are 
for us at present the most important exceptions, and may be 
considered first. Here the apex both of root and stem appears 
to have a single initial ; it is to be noted, however, that both 
these members are buried deeply underground in the living 
plant, and are so protected by their habit; but the leaf 
bearing the sporangia is aerial and exposed, and it is to be 
noted that its structure is comparatively bulky, and that in 
its early stages no single initial is found, while the sporangium 
is typically eusporangiate. Accordingly, it would appear 
that here there is a correlation even in the parts of an in- 
dividual plant between exposure to dry air and a greater 
complexity of meristems on the one hand, and on the other 
between protection from evaporation and simplicity of structure 
of the meristems. But while recognising these facts, care 
must be taken that they be not overestimated. A comparison 
of the table above given will show that the case of the 
Ophioglossaceae is the exact converse of that for the Osmun- 
daceae and Marattiaceae : in these the leaf which is aerial and 
exposed is the most conservative of the structure typical of 
1 See Holle, Bot. Zeit. 1875 ; as far as my own observations go, they bear out 
those of Holle. 
