PALEOZOIC SEED STUDIES: A NEW PENNSYLVANIAN PACHYTESTA FROM SOUTHERN ILLINOIS

Pachytesta stewartii, a new species found in Middle Pennsylvanian coal ball deposits in southern Illinois, is 2.5 cm long and approximately 1.5 cm in width at its greatest diameter. Commissured ribs are pronounced near the apex and progressively less distinct toward the base. The integumentary system is delimited into 3 regions: outer sarcotesta, middle selerotesta, and thin endotesta. Conspicuous in the new species is a pronounced basal extension with an enclosed chamber that may be the result of decomposition of thin-walled parenchyma cells. Relationships with other species and possible significance of the chalazal chamber are discussed. FIRST described bv Brongniart (1874), emended by Hoskins anid Cross (1946b), and later by Stewart (1951), the genus Pachytesta as now delimited includes large, radially symmetrical seeds that possess a multiple-layered integument, stalked or sessile nucellus attached only at the base, vascularized nucellus and integument, and, in some species, distinct radially extending commissured ribs. The following description of a new species is based on sev%eral specimens discovered in coal ball material collected at the Sahara Coal Company mine near Carrier Mills, Illinois (Sec. 30; T 9 S, R 4 E, Harrisbuirg, Quadranigle). These deposits. according to the most recent classification of Pennsylvaniani rocks in Illinois, are Middle Pennsylvanian in age (Kosanke et al., 1960). DESCRIPTTo\T-CGeneral morpholoqy-The new seeds are relatively large, approximately 2.5 cm long and about 1.5 cm wide at the greatest diameter. Three commissured ribs are present near the apex of the seed, becoming less pronounced toward the base. Three parts of the integument are preciselv delimited by cellular orientation and structure. The most conspicuous feature of the new species is a large tapering base possessing a hollow chamber. Integqument-In the new seed, zones of the integument are similar to those founid in other members of the genus. There is an outer sarcotesta, a middle, apparently fibrous, 2-parted selerotesta, and a thini endotesta. Thickness of the integument -varies throughout the length of the seed; it is thick in apical and basal reg,ions and thinner toward the middle. 1 Received for publication July 18, 1963. The senior author wishes to express sincere appreciation for assistance awarded by the Committee on Grants-inAid of Research of Sigma Xi-RESA. Research was also financed, in part, by NSF Grant GB 420 to the junior author. In the usually poorly preserved sarcotesta are irregularly shaped, thin-walled cells (Fig. 9, 12) that often measure 70 X 140,u, although sizes up to 400, are not uncommon. In the petrified material these jigsaw-puzzle-shaped cells often contain an opaque material. A thin epidermis probably covered the seed at some stage during its ontogeny; however, the incomplete preservation of the sarcotesta makes it difficult to recognize. The variable thickness of this layer is apparently the result of changes that occurred during fossilization. A thin coalified laver is often situated between the sarcotesta and the selerotesta, evidently the result of partial decomposition and separation of these tissues. In places where it is organically attached to the seed body, the sarcotesta is approximately 1.5 mm thick. Large patches of this tissue in association support the assertion that it was much thicker prior to fossilization. A sclerotesta makes up the middle portion of the integument. The outer portion, about a quarter of the thickness, is composed of a monostromatic layer of cells that are elongated and oriented perpendicular to the long axis of the seed (Fig. 9-11). Each of these cells measures 35 X 145,, with a wall thickness of approximately 6,u. This portion of the selerotesta remains uniform in thickness throughout, and in orientation and histology appears similar to the outer sclerotic layer in the genus Stephanosperi-mun (Hall, 1954). The remaining portion of the selerotesta is characterized by similar elongated cells, but of larger size. These cells measure 50,u in diameter and approximatelv 400,u in length (Fig. 9-11). Furthermore, these cells are oriented in a planie parallel with the long axis of the seed (Fig. 9), except in the chalazal region where they take on a more tortuous course and are sectioned in various planes (Fig. 1, 4, 8). The substantial increase