774 MR R. KIDSTON AND MR D. T. GWYNNE-VAUGHAN ON 



in a section taken about 5 mm. above the one we possess, nor in another taken about 

 the same distance below. In face of these facts, we are only able to regard it as an 

 unaccountable anomaly. 



The thin-walled inner cortex of the stem is beautifully preserved, and is surrounded 

 by a comparatively narrow sclerotic outer cortex (PL IV., figs. 22 and 23, i.e. and o.c), 

 but the fossil only includes a very small portion of the coating of leaf-bases. Each 

 petiole has a sclerotic ring of its own, and a few isolated strands of sclerenchyma are 

 scattered in the parenchyma lying between it and the leaf-trace. The concave surface 

 of the latter is also bordered by a broad zone of the same sclerotic tissue (PI. IV., fig. 

 23, It. 1 ). The leaf-bases certainly possessed parenchymatous stipular wings, but even 

 the outermost is cut too near the stem to show the arrangement of the stipular scleren- 

 chyma — if, indeed, they contained any at all. 



The Root. 



The roots arise directly upon the xylem of the stem, just below the angles of the 

 leaf-gaps. The xylem strand of the root appears to run downwards within the phloem for 

 some distance before it becomes free from the stele of the stem. The xylem of the root 

 is at first rounded in section, and without definite protoxylem elements, but further out 

 it becomes elliptic and diarch. The root obtains a cortex of its own before it has left 

 the tissues of the stem. It consists of two zones, an inner cortex of thin-walled cells 

 and a broad sclerotic outer cortex. 



Theoretical Considerations. 



According to Jeffrey (8) and Faull (9), the Osmundacese present a series of reduced 

 structures, so far, at least, as their vascular systems are concerned. This opinion is 

 based upon an attempt to explain the presence of the internal phloem and endodermis 

 discovered by Faull at the inner margin of the xylem ring of Osmunda cinnamomen. 

 The vascular system of this plant is supposed by these authors to have degenerated 

 from a dictyostelic cylinder, the leaf-gaps in which have been reduced to the so-called 

 medullary rays. In Osmunda cinnamomea, the internal phloem and endodermis of 

 the confluent meristeles is still retained at any rate in the neighbourhood of the 

 branchings. In the other species of the order, the reduction has gone so far that 

 these tissues have entirely disappeared ; except, perhaps, in Todea hymenophylloides, 

 where, according to Seward and Ford (I.e., p. 249), indications of the internal endo- 

 dermis are still occasionally to be found. This theory has met with strong opposition 

 from subsequent writers, Boodle (10), Seward and Ford (I.e., p. 255), and Chandler 

 (11), who base their objections chiefly upon the absence of confirmatory evidence in 

 the stem of the young plant. We entirely agree with their criticisms, and prefer to 

 regard the Osmundaceous type of vascular system as directly derived from a primitive 



