Farmer —On Isoeies lacustris, L. 45 
speaking, but little developed, and there Is moreover In this 
plant no apparent need of special protection, especially as the 
older leaves so securely shelter the younger ones. It is only 
in exceptional cases that I have met with any prolongation of 
a few of its terminal cells at all comparable with that in 
I. velata , and the whole structure Is smaller and simpler than 
in that plant. It is of course known that the slow-growing 
leaves of Ferns are commonly provided with some protective 
structure, and they may be regarded as representing the means 
for satisfying In a simple manner those requirements which in 
the higher plants involve the modification of potential foliage- 
leaves 1 , stipules, etc. into scale-leaves. Without desiring to 
press the point too far, It may be noticed that these modifi- 
cations are especially characteristic of the highest orders of 
plants, i. e. Phanerogams, and that in the lower members, such 
as Cycasj in which the early steps may be perhaps supposed 
to be observable, the arrangement is not such as to suggest 
that economy of material which is commonly to be seen in 
adaptive modifications. The stipules of Marattia and the 
curious structures described by Holle 2 for the Ophioglossaceae 
are familiar examples of the more complicated kinds of pro- 
tective structures met with amongst the Vascular Cryptogams, 
whilst the simpler forms of the series are represented by the 
r amenta of so many Ferns. Much has been made of the ligule 
in Isoetes as indicating some affinity with Selaginella in which 
a similar structure occurs, but the two are In reality very 
different ; that of Selaginella arises not from one cell, as in 
Isoetes , but as a multi-cellular protuberance ; the mature struc- 
ture Is, moreover, not nearly so complete as in Isoetes , especially 
as regards its insertion. The point, however, which specially 
weakens the grounds for basing any theories of affinity on the 
common possession of the ligule by the two genera, is the 
much later development of this structure in Selaginella than 
In Isoetes . And even if this were not the case, outgrowths of 
a similar nature and belonging to the same category are so 
1 Goebel, Beitr. z. Morph, u. Physiol, des Blattes, Bot. Zeit. 1880. 
2 Holle, Ueber Ban u. Entw. d. veg. Organe d. Ophioglosseen, Bot. Zeit. 1875. 
