360 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



(1946), and especially by Sahni (1948). The branched stems {Pentoxylon) are 

 polystelic; the primary bundle of each stele is surrounded by a zone of coniferlike 

 secondary xylem. The taeniopteroid leaves {Nipaniophyllum) seem to have pos- 

 sessed syndetocheilic stomata and vascular bundles of the cycad type. The fe- 

 male organs {Carnoconites), borne terminally on branched stalks, are conelike 

 with densely packed, sessile ovules. The Pentoxyleae combine features sug- 

 gestive of the bennettites, cycads, and conifers, but the morphology of the cone 

 and the stem anatomy indicate an isolated position. Gaussen (1944-1952), how- 

 ever, has tentatively referred them as a special subgroup to the Bennettitales. 



Cord AIT ALES 



Frentzen (1931) investigated paleozoic woods of the form-genus Dadoxylon, 

 all possessing in the radial walls of the secondary tracheids relatively small, 

 crowded bordered pits, either primitively biseriate to multiseriate, circular to 

 hexagonal in outline, and arranged alternately, or else uniseriate with more or 

 less markedly flattened outline above and below (araucarian pitting). This type 

 of wood is a feature of the Cordaitales, but it also occurs in other gymnosperms 

 (cf. Boureau, 1949; Gaussen, 1952). Two groups are discernible: one has the 

 radial walls of its tracheids covered by bordered pits, which the other has not. 

 The latter appears to represent the conifer family Lehachiaceae. Traverse 

 (1950) studied the primary vascular body of Mesoxylon. Contrary to previous 

 opinions, the sequence of centripetal and centrifugal primary wood in the leaf 

 traces was the same in the leaf base and in the stem. Our knowledge of the 

 stems of the Pityeae was summarized by Arnold (1947). In a species of Pitys, 

 Gordon (1935) investigated the vegetative organs anatomically. Re-examination 

 of the whole genus served to bring Pitys, Archaeopitys, and Callixylon into close 

 relationship, to remove them from the cordaites, and to indicate a lyginopteroid 

 origin for the group. Cribbs (1938, 1939, 1940) discovered stems with various 

 combinations of pityean and calamopityean features. Conclusive proof that 

 roots of the Amyelon type belong to cordaites was given by Andrews (1942). 

 Reed and Sandoe (1951) described the superficial epidermal pattern in com- 

 bination with the internal anatomy of the same cordaitean leaf. 



Recent investigations have materially contributed to the elucidation of the 

 morphology of the male organs. Hirmer (1932) described the anatomy of the 

 inflorescence axis, including the origin and course of the vascular bundles des- 

 tined to innerve the strobili. Florin (1938-1945, 1951) found that the male 

 short shoots are of the nature of strobili or "flowers." Their axes carry spirally 

 arranged, leaflike scales, some of which are simple and sterile, while the re- 

 mainder terminate in a cluster of four to six upright microsporangia. The single 

 sporophyll bundle is bifurcated repeatedly at the apex. The microsporophyll ap- 

 pears to derive from a primitive radial and dichotomizing sporangial truss, the 

 ultimate branches of which formed erect, elongate, and cylindrical sporangia. 

 The female organs (Florin, loc. cit.) are built essentially in the same way, and 

 have strong main axes, carrying alternating bracts in two opposite rows and 

 axillary strobili. There is an earlier, more primitive type, characterized by 

 elongate megasporophylls projecting from the apical region of the strobilus, 

 and a later, reduced type, characterized by very short, unbranched megasporo- 



