218 
aL 
resent a primitive synthetic group from which both mosses (Bryo- 
— 
phyta) and vascular plants were derived. Whether they are prim- 
itive and ancestral or merely ancient and simple they serve to give 
a very good idea of what we might expect to be the organization 
of the most primitive land plants. 
The Psilophytales are the most ancient known representatives 
of a phylum to which the Lepidodendrons and Sigillarias of the 
coal swamps belong, and which survive in modern floras as herba- 
ceous cClubmosses and quillworts. 
The fourth Devonian plant, shown in the right hand corner of 
the transparency, has been christened //yenia, and is supposed to 
be a middie Devonian progenitor of the Horsetail group (shown 
in transparency No. +). Two species are known, one from Nor- 
way and the other from Germany. The stems are less than an 
inch in diameter, not jointed, and fork dichotomously. The leaves 
are forked and are borne on the stem in whorls of three or four. 
The fructifications are loose terminal cones without bracts and 
with whorled forked sporangiophores (stalks bearing sporangia), 
each fork bearing two or three sac-like sporangia. 
3efore the close of the Devonian these ancient simple types were 
largely replaced by more complex types such as Archacopteris, 
Pseudoborma, Sphenophylinn, Cordaites (Callixylon), Proto- 
lepidodendron, and Bothrodendron (Cyclostigma), which are illus- 
trated and will be briefly described in the account of the next of 
this series of transparencies (No. 4). 
4. Tree Clubmosses 
This transparency, showing four different genera of the Tree 
Clubmosses, portrays a history extending from the upper Devonian 
to the close of the Paleozoic, and represented by a few hold-overs 
in the earlier Mesozoic. All are ce related to the existing 
Clubmosses, and those who look at the past from the standpoint 
of the modern systematic botanist sometimes include these varied 
extinct forms in the modern Clubmoss order, Lycopodiales. — It 
s, however, more logical to group all of these scale-leafed forms 
in a separate phylum—the Lepidoy i and to recognize their 
undoubted distinctness from the ern and the Horsetail groups. 
The Tree Clubmosses were a great group characterized by small, 
