86 Gibson. — Contributions towards a Knowledge of 
Farmer says, £ the relationship between the two is at the best 
but very remote, so different are they in all other important 
characters ; to endeavour, therefore, to unite them on account 
of the presence of a ligule in each of them, even if this structure 
were more similar in the two plants than as a matter of fact is 
the case, is like an attempt to establish an affinity between 
Rosaceae and Cupuliferae on the ground that stipules are 
common to both orders.’ 
My own view of the homology of the ligule in Selaginella is 
briefly that it is a specialized ramentum, such as one finds so 
commonly in the Pteridophyta and in the Hepaticae. I base 
this conclusion on certain facts with regard to the structure 
and development of the ligule itself. In the first place, the 
ligule is developed very early in the history of the leaf, and 
is fully developed long before the leaf to which it belongs 
has reached maturity. Farmer affirms that the ligule in 
Selaginella is much later in development than in Isoetes 
(/. c., p. 45). I have not examined the development of the 
ligule of Isoetes, but comparison of Farmer’s drawings and 
my own sections of the growing-point of Selaginella does 
not seem to me to bring out any well-marked difference 
between the two ’structures in this relation. The apical 
bud in Selaginella is very dense, and the leaves are very 
closely packed, the whole growing region being extremely 
short. It is true that the ligule is comparatively small as 
compared with even the young leaf ; but the close packing of 
the leaves may, and probably does, very materially aid in 
protecting the growing-point from desiccation. Farmer draws 
attention to the same fact in Isoetes lacustris, where c the ligule 
is, comparatively speaking (with I. velata), 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.’ 
Then again the vascular bundle to the leaf runs in close 
relation to the glossopodium, and may, as has been shown 
above, form a more or less distinct cup of tracheides around 
it. An adequate supply of water to the ligule is thus pro- 
vided for. 
