38 MORPHOLOGY OF GYMNOSPERMS 



in the character of the pollen grains (described below). Oliver (85) 

 sees in Physostoma elegans, with its "tentacles" and "secretory 

 nucellar zone," the most primitive condition. The following series' 

 on the basis of freedom or coalescence of the integument lobes is 

 attractive: in Physostoma they are free and the body of the seed is 

 ribbed; in Conostoma the body is ribbed below and smooth above, 

 and the integument lobes are united, but show a tendency to separate; 

 in Lagenostoma the body is completely smooth and the integument 

 lobes are completely united to form the characteristic chambered 

 "canopy." The numbers of the units of integument structure vary 

 as follows: 10 in Physostoma elegans, 9 in Lagenostoma Lomaxii, 

 8 in L. ovoides, 7 in Conostoma oblonga, about 6 in L. Kidstonii (P. 

 Kidstonii). 



The characters of Lyginodendrineae given in the preceding pages 

 make it possible to outline the probable features of the group. Scott 

 (87) has suggested in effect the following tentative description: leaves 

 fernlike (Sphenopteris or Pecopteris); stem monostelic and with 

 xylem mesarch; leaf trace and main leaf bundle single or double, 

 concentric in the petiole; reproductive organs on somewhat modified 

 pinnae; microsporangiateorgansof the Cro^^o^/jeca type; seeds radial, 

 cycadean, with nucellus and integument free only in the region of the 

 nucellar beak and with a singular vascular system, and often inclosed 

 (singly or several together) in a cupule. 



Medullosa. — In 1904 Kidston (44, 45) announced the discovery 

 of three fragments of Neuropteris heterophylla, each of which bore a 

 seed "as large as a hazelnut" on a pedicel terminating a pinna (fig. 

 40). These seeds are about 3 cm. long, oblong in outline but tapering 

 to a point, and invested by a fibrous envelope. Their internal struc- 

 ture is not known, but they belong to a general type of paleozoic seeds 

 quite different in structure from the Lagenostoma type. The relation 

 of the seeds to the fronds is the same as in Lyginodendron, but there is 

 no evidence of such extreme dimorphism, the seeds being terminal 

 on the naked tip of a pinna which otherwise does not differ from the 

 ordinary pinnae. That this Neuropteris is the foliage of a Medullosa 

 is clear, and there is enough evidence to indicate that all the members 

 of this stem genus were seed-bearing, and that the seeds were borne 

 terminally upon more or less modified pinnae. 



I The description of Sphaerostoma is not yet available. 



