368 TRANS, ST. I.OUIS 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 l?ase 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 \ to i line long in /. melanopoda\ i 

 to 2 lines in /. pygmcea, Tuckermani, echinospora, and saccha- 

 rata; \\ to 2? lines in I. lacustris, Bolanderi TunA Jlaccida; 

 often a little larger in /. Butleri and Nuttallii; 2 to 4 lines in /. 

 riparia, Engelmanni, melanopoda^ and Cubana; and in larger 

 forms of /. Engehnanni 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 (z^e/e//;?) ; 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. /. 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 (jnicrospores or androspores) ; these 



