304 . ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



of the Pecopteris type, arranged in crowded spirals (Psaronius poly- 

 stichi = Caulopteris impressions), in four vertical rows {Psaronius 

 tetrastichi) or in two opposite vertical rows (Psaronius distichi= 

 Megaphyton impressions). Specimens of Psaronius were probably 

 the earliest known fossil plants with structure preserved since pol- 

 ished slabs of the trunks were in considerable vogue during the 

 eighteenth century as decorative objects under the names of "staar- 

 steine " or starling stones because of their speckled appearance 

 (Psaronius has the same meaning), dependent on their anatomical 

 structure. A very large number of species have been described from 

 the Upper Carboniferous and Permian. They have been favorite ob- 

 jects of histological investigation since the days of Corda (1845), 

 since they are common in a petrified condition in Saxony, France, 

 and elsewhere. Anatomically, the stems have a complex system of 

 laterally elongated, concentric curved steles of scalariform tracheids 

 surrounded by phloem and immersed in a parenchymatous ground 

 mass with some sclerotic bands below the leaf gaps. 



Some of the polyarch roots show secondary wood, but none has 

 been observed in the stems, the central one cauline and the outer 

 ones giving off numerous leaf traces and adventitious roots. Outside 

 the sclernchymatous region which bounds the stem proper is a very 

 broad zone, formerly thought to be cortical, consisting of closely 

 packed adventitious roots embedded in a dense felt of hairs which 

 spring from both the stem and the roots. 



The petioles usually show a single horseshoe-shaped trace, al- 

 though sometimes a second lies within the first. The occasional 

 presence of lacunae in the root cortex of some of the species suggests 

 a swampy substratum. 



Pecopteris fronds represent the one type among the many familiar 

 fern-like fronds of the Paleozoic which are so abundant in the roofing 

 shales of the coal seams that is frequently found in a fruiting con- 

 dition. Some have been demonstrated to have been borne upon 

 Psaronius stems and this is probable of the majority. The fructi- 

 fications are of a variety of types. Those known as Asterotheca 

 had large synangia in two row r s, one on either side of the median 

 vein on the under surface of the pinnules, each consisting of five 

 or six sac-like confluent sporangia forming a close ring. Other 

 confluent synangia known as Ptychocarpus characterize an Upper 

 Carboniferous and Permian series of Pecopterids. These synangia 

 consist of five to eight sporangia united laterally to form a close ring 

 and adherent to a central receptacle and embedded in continuous 

 enveloping tissue. They discharge their very numerous small spores 

 through apical pores, and greatly resemble the arrangement in the 

 modern genus Kaulfussia. A third Paleozoic type is Danaeites and 



