220 
(Angiosperms) the ovules and resulting seeds are enclosed in an 
ovary or carpel, and the pollen falls on a receptive surface (stigma) 
where it sprouts and sends a tube through the tissues of the pistil 
and thus carries the sperm-cells to the enclosed egg-cell. The pol- 
len may be wind-distributed, but more often the agency 1s flying 
insects or, less often, birds. Angiosperms are geologically much 
more recent than Gymnosperms, and are the dominant plants of 
existing floras. 
Four types of gymnosperms are shown in the transparency de- 
voted to Paleozoic Gymnosperms—Porox\lon, Cordaites, Walchia, 
and Baiera. 
Porox\ilon, at the left, represents a late Carboniferous and Per- 
mian type which is known chiefly by the anatomy of petrified stem 
fragments, and there is some uncertainty regarding its leaves, 
seeds, and catkins. The plants are thought to have been slender- 
stemmed, much like bamboos in appearance, with very large, flat, 
slightly fleshy, parallel veined leaves. They are considered to be 
related to Cordaites, the usual treatment being to consider the order 
Cordaitales as divided into three families—Poroxyleae, Cordaiteae, 
and Pityeae. 
Cordaitcs was exceedingly abundant and varied at several hori- 
zons in the Paleozoic, and the synthesis of a study of impressions 
of their foliage and fructification, pith casts, and petrifactions en- 
ables us to draw a satisfactory picture of their general appearance 
and habit, although as yet it is usua 
— 
ly im 
— 
ossible to correlate spe- 
cific foliar impressions with petrified stems and seeds. 
They were tall and relatively slender trees, with trunks that were 
frequently over one hundred feet in height and unbranched, except 
at the crown, where their spirally arranged foliage of simple and 
often large parallel veined leaves was displayed. Leaf-form has 
been used as a basis for the three form-genera: Fucordaites, with 
spatulate biunt-tipped leaves, often several inches in width and two 
or three feet in length; Dorycordaites, with pointed leaves ap- 
proaching those of Eucordaites in size; and Poacordaites, with 
narrow linear leaves. Phe parallel venation, unbranched in Poa- 
cordaites, but repeatediy forked in Dory- and Eucordaites, suggest 
monocotyledon foliage, and the early writers consequently con- 
sidered Cordailes as a monocotyledon. Both the wood structure, 
