of Goal-Measure Plants. 153 



Binney's stems with the Lepidophloios fidiginosus type, the sections 

 also demonstrate (i) that the so-called duplex nature of the leaf- 

 traces cannot be accepted as a distinctive feature of L. Harcourtii, 

 and (ii) that the strand of tissue accompanying the xylem of the 

 leaf-traces does not exhibit the characters of bast-fibres. A com- 

 parison of Binney's sections with examples of the true L. Harcourtii 

 leaves no doubt in my mind as to the identity of the structure of 

 the leaf-traces in the two forms. If the view elsewhere expressed 

 that the large Dalmeiry stem may be regarded as an example of 

 L. Harcourtii be correct, we must speak of Witham's species as a 

 type of Lepidodendroid stem in which secondary thickening began 

 at an unusually late stage. In Lepidophloios fuliginosus, which in 

 most respects appears to be practically identical with L. Harcourtii, 

 the development of secondary stelar tissues began at an earlier 

 period. 



The chief features of more general interest exhibited by the 

 Sections 1 — 4 are to be found in the structure of the tissues im- 

 mediately external to the xylem, and in the nature of what has been 

 spoken of as the secretory zone. In the above description no mention 

 has been made of the presence of typical phloem ; the excellent 

 preservation of even the most delicate cells justifies the belief that 

 had phloem tissue been originally present, it would not have been 

 likely to have suffered decay to such an extent as to render its 

 preservation or recognition impossible. The xylem of the stem is 

 surrounded by a fairly broad band of short and slightly flattened 

 cells constituting a tissue to which the term meristematic zone has 

 been applied ; the reason for this appellation is that in some of the 

 sections certain cells in this region are in a state of meristematic 

 activity, and an identical band of short- eel led parenchyma in the 

 large Dalmeny stem was found to be the seat of active cell- 

 formation. Whether or no this tissue is appropriately named, it is 

 clear that it bears but little resemblance to what we are accustomed 

 to regard as cambium in recent plants. It is moreover very much 

 broader than the ordinary cambial tissue of Dicotyledons or Gymno- 

 sperms, or of Botrychium among the Vascular Cryptogams. The 

 formation of secondary tissues has scarcely begun in the sections with 

 which we are at present concerned, but such traces as exist favour 

 the view expressed at greater length elsewhere, that the method of 

 secondary thickening in Lepidodendroid plants differed considerably 

 from that with which we are familiar in recent plants, or in such 

 fossil genera as Calamites, Lyginodendron, Sphenojjhyllum and 

 others. 



Beyond the meristematic region there is a characteristic band 

 referred to as the secretory zone. This tissue forms a well- 

 marked feature in stems of L. fuliginosus, L. Wunschianus, L. Har- 

 courtii and other species ; the elements composing it do not 



