3 68] 
TRANS. ST. ROUIS ACAD, SCIENCE. 
leaves soon after their maturity in autumn, some of our terres¬ 
trial ones even already in summer. 
The broad membranaceous sheathing base of the leaf is with¬ 
out air cavities, stomata, or bast-bundles ; in sterile leaves it 
gradually contracts into the leaf itself. Those leaves are usually 
sterile which develope at the beginning and the end of the sea¬ 
son. The fertile leaves have in their base an excavation which 
bears the spore-case, sporangium, adnate with its back to the 
midrib. Above this excavation, and separated from it by a deep 
transverse depression or slit, we find a stipule-like organ of tri¬ 
angular more or less elongated shape, cordate at base, appressed 
to the leaf, which is termed the ligula; it is small, and in not 
very fresh leaves often mutilated and difficult to make out. The 
morphology of these parts is obscure and their diagnostic value 
not great. 
The sporangium is oblong or circular (both forms often seen 
in the same species), from 1 to i line long in /. melanopoda ; I 
to 2 lines in /. pygmcea, Tuckermani, echinospora , and saccha - 
rata ; iT to 2? lines in I. lacustris , Bolanderi and Jlaccida; 
often a little larger in I Butleri and Nuttallii; 2 to 4 lines in I. 
riparia , Engelmanni , melanopoda , and Cubana; and in larger 
forms of d. Engelmanni I have seen it* 8 to 9 lines long. It is 
somewhat flattened, and often slightly concave on the ventral 
side ; it is entirely naked or (the usual case) it is on its sides and 
principally upwards partially covered by a fold of the ventral side 
of the leaf-base, the veil {velum) ; in a few species (I. Jlaccida , 
melanopoda , and Nuttallii) this fold extends over the whole 
sporangium, completely covering it (velum completum) . The 
sac of the sporangium is composed of two layers of cells; the 
outer, epidermidal, layer consists of elongated, often variously 
bent or hooked and curiously interlaced cells, mostly thin-walled 
and transparent ; in some species (e.g. I. riparia , I. sacchara - 
ta , I. melanopoda') groups of brown, thick-walled, (so-called) 
sclerenchym-cells are mixed with the transparent ones, giving 
the spore-case a dotted appearance visible even to the naked eye. 
The spore-case is traversed by numerous parallel strings. 
Some sporangia, called macrosporangia , contain larger or 
female spores (macrospores or gynospores) , others are filled with 
the minute or male spores (microspores or androspores) ; these 
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