Series I], PTERIDOPHYTA. 
By Lucien M. UNDERWOOD, 
Vascular, mostly herbaceous plants. Reproductive bodies consist- 
ing of spores variously borne on the leaves, or in special receptacles, 
separate or clustered on the stems. Spores on germinating producing 
a liverwort-like prothallus on which the sexual organs, consisting of 
archegones and antherids, are borne. From the fertilized archegone 
arises the asexual or mature plant. Contains (in our limits) seven 
orders, distinguished as follows: 
ARTIFICIAL KEY TO THE ORDERS. 
* Heterosporous, i. é., spores of two kinds, 
+ Terrestrial mess-like plants. 
Selaginellacee, Leaves 4-ranked or many-ranked; spores borne in the axils of leaves 
which form more or less distinet terminal spikes .........----....-.-...----). 597 
+ + Aquatics, rooting in mud, . 
Isoetacew. Leaves awl-shaped, arising from short bilobed trunks; spores borne in 
oval sporangia which are inclosed in the base of the leaves.......-.-------- p. 558 
Marsileacew, Leaves filiform or quadrifoliate, rising from more or less creeping root- 
stocks; spores borne in oval sporocarps....-..------.---- eee eee eee eee ee eee p. 560 
+++ Aquatics, floating. 
Salviniacee. Leaves distichous on a more or less branching stem; sporocarps ovoid 
or globose, borne in the axils of the leaves ...... cee eee en cece eee eee eeee p. 559 
* * Tsosporous, t. e., spores of one kind, 
Equisetacee, Rush-like plants, with spores borne in sporangia under shield-shaped 
scales which are crowded in terminal spikes.......---..-------------------- p. 559 
Filices. Fern-like plants, with circinate vernation; spores collected in reticulate 
sporangia, borne in clusters on the back or margin of the leaf or in spikes or 
panicles ....... 22-22-20 2-25 eee eee eee eee ee ee cee cee cree eens p. 560 
Ophioglossacee, Small somewhat fleshy plants with erect or merely inclined verna- 
tion and with spiked or panicled sporangia which open by a transverse slit. ~p. 568 
SELAGINELLACEZ. 
Plant body leafy, terrestrial, moss-like, with more or less branching 
stems and scale-like leaves: sporangia one-celled, solitary, borne in 
the axils of the leaves, some containing macrospores and others micro- 
spores, 
557 
