1 8 WEISS, The Parichnos in the Lepidodendracece. 



that of the stem by any strand of thin-walled parenchy- 

 matous cells, provided with intercellular spaces capable 

 of conveying air to the rootlet? Is there anything 

 corresponding to a parichnos strand of a leaf? As a 

 matter of fact this is the case, and Fig. 4 of the Plate shows 

 the group of small parenchymatous cells accompanying 

 the rootlet bundle on its way outward through the outer 

 cortex in a Stigmaria, described by Hick ('92), under the 

 name of Xenophyton. An examination of a series of 

 sections shows that this parenchymatous group is in con- 

 tinuity with the mid-cortex of the Stigmarian axis, and it 

 must therefore be regarded as the equivalent of the 

 parichnos strand of the leaf cushion. In my re-description 

 of Xenophyton (:o2), I mentioned the continuity of this 

 small-celled tissue below the rootlet bundle with the mid- 

 cortex, but the correspondence of it with the parichnos of 

 the leaf cushion did not then occur to me. It will be 

 noticed that this " parichnos " of the rootlet running on 

 the underside of the rootlet bundle, is really on the 

 morphologically upper, i.e., apical side of the Stigmarian 

 axis, and consequently on the xylem side of the bundle, 

 not on the phloem side, as in the case of the parichnos, 

 which runs in connection with the leaf trace. This strand 

 of middle-cortex cells runs right through the outer cortex 

 and periderm to the " cushion " from which the rootlet 

 springs, and there passes into the close parenchyma of 

 which the cushion is largely formed. No doubt this 

 parenchyma had intercellular spaces ; and indeed in very 

 well-preserved Stigmariae they are apparent, though very 

 small, and through them communication was set up between 

 the lacunar mid-cortex of the Stigmarian axis and that of 

 the rootlet. Thus air could be brought to reach the rootlets 

 or Stigmarian appendages, which we believe to have been 

 embedded in a water-logged medium. This correspondence 



