LEPIDODENDRIDS 269 
482. Allied to the Club-mosses are the arborescent 
Lepidodendrids (Order Lepidodendrales) which were 
abundant in the Paleozoic period, and which disappeared 
in the Mesozoic. We have fragmentary fossils of the 
sporophytes, which were large dichotomously branched 
trees, sometimes 30 meters high and a 
meter in diameter. There was a large 
central vascular bundle, which how- 
ever formed a peripheral cambium 
so that the stems increased their di- 
ameter much as in the case of higher ..f‘ 
plants. The stems and branches ric. 145.—Lepidoden- 
were thickly clothed with pointed (707, Gporophyte, spor- 
leaves a decimeter or more in length, 
and when these fell off they left large scars of charac- 
teristic shape and arrangement. 
483. The fossil remains of the spore-bearing cones, of 
which many specimens have been found, indicate that 
they contained two kinds of spores. Hence it is certain 
that the Lepidodendrids were allied to the Club-mosses. 
The more common genera are Lepidodendron, and 
Sigillaria. 
Laboratory Studies. (a) Secure a few fresh or alcoholic 
specimens of various kinds of Lycopods in fruit. Ground 
Pines may be collected in many places in the eastern United 
States. The Club-mosses may be obtained in plant-houses. 
(6) Make cross-sections of the stems, and study the vascular 
bundles in Lycopodium where they are imbedded in a thick 
mass of fibrous tissue. Examine the leaves, noting the small 
vascular bundle in the midrib. Study the epidermis, which 
contains numerous breathing-pores. 
(c) In like manner study Selaginella. 
(d) Carefully remove a sporophyll from a cone of Lycopo- 
dium, and study the sporangium and spores. Further exami- 
nation will show that the spores are of one kind only. 
