PTERIDOSPERMZE, or PTERIDOSPERME/E, in paleobotany, a class, co-ordinate with Gymnosperme and An giospermee, of fossil Paleozoic fern-like plants, including all such which on the evidence avail able appear to have been reproduced by means of seeds. Potonie called this class Cycadofilices. And some paleobotanists even regard the group as a phylum, or primary division, and not as a class; and to this phylum they then apply the name "Pteridospermaphyta° ; but the idea of the group's being a class is gaining favor. A sin gle plant of the group is a The cases in which the evidence available ap pears to be decisive are but few; and to these have been applied the names which follow : (1) Lyginodendron oldhamium; (2) Neuropteth boterophylla; (3) Pecopteris Pluckeneti; (4) Aneimites fertilis; and (5) Aneitnites tenui folilts.
In the first named pteridosperm, Lyginoden dron oldhamium, the structure both of the vege tative and reproductive organs is known; and the evidence from comparison and association is sufficiently strong. So identification is cer tain and easy. And in the other cases there is direct proof of continuity between seed and plant; but only the external characters are known. In a great number of forms amount ing to a majority of the Paleozoic plants of fern-like habit, the evidence — such as it is is in favor of their having possessed seeds. They are pre-eminently plants resembling ferns in habit and in many anatomical characters but bearing seeds of the Cycadean type. Seeds and microsporangia,— or pollen sacs of the anthers,— are low on the fronds, and only slightly modified as compared with the vegeta tive leaves in Pteridosperm a. Pteridospermae, of which only a few examples have so far been considered by paleobotanists, evidently consti tuted a group of vast extent in Paleozoic times. In a large majority of the fern-like fossils of that period the evidence is in favor of repro duction by seeds rather than by the cryptogamic methods of true ferns. The whole class of Pteridosppeermae though clearly allied to the typical Gymnospertn may be kept distinct for the present on account of the relatively primi tive characters shown in the anatomy and morphology of the former. During recent years
a number of Carboniferous and Permian plants have been very thoroughly investigated in the light of modern anatomical knowledge, and as a result it has become clear that in those times a large series of plants existed inter mediate between the modern Gymnosperma,— especially the Cycads,— and the true ferns.
The first definite evidence of the mode of reproduction of Lyginodendron oldhamium was due to the studies of F. W. Oliver, who in 1903 identified the seed Lagenostoma Lomaxii by means of the glands on its capsule, which agree exactly with those on the associated leaves and stems of the plant. No similar glands are known on any other Palwozoic plant. Lagenostoma Lomaxii is a small, barrel-shaped seed, 5.5 by 425 mm. when mature, enclosed in a husk or capsule, which completely envelops it when young but ultimately opens. The male organs of Lyginodendron oldhamium were dis covered by Kiddon, a year or two after the seeds were identified. They are of the type known as Crossatheca, formerly regarded as a Maratteaceous fructification. This is the first case in which the pollen-bearing organs of a Pteridosperm have been identified. It will be noticed that while the seeds of Lyginodendron oldhamium were of an advanced Cycadean type, the microsporangiate organs were more like those of a fern, the reproductive organs thus showing the same combination of characters which appears in the vegetative structure. It must here be mentioned that the family Calamo pityeal, allied anatomically to Lyginodendrex, is of the Devonian and Lower Carboniferous age.
Bibliography.— Potonie,