46 The So-called Phloem of Lepidodendron. 
I have so far entirely failed to discover any evidence of the 
existence of a tissue which can be called secondary phloem in 
Lepidodendroid stems. The broad meristem-zone in the Dalmeny 
stem is succeeded externally by the secretory zone, which exhibits 
no signs of additions made to it by cambial activity. 
Dr. Scott 1 has expressed the view that the cambium in 
Lepidodendron did not produce much secondary phloem; I am 
inclined to go further and to express the opinion that true secondary 
phloem has not been recognised. This apparently one-sided activity 
of the meristem zone suggests a comparison with Botrychium 
Virginianum, which is described by Dr. Jeffrey 2 as characterised by 
the absence of secondary phloem. 
It is impossible to deal adequately with the various points 
connected with the question of phloem without unduly extend, 
ing the length of this article, but 1 wish to emphasize the 
need for further information as to certain anatomical features of the 
genus Lepidodendron. Dr. Scott has also drawn attention to some 
points connected with the cambium which require explanation, and 
he so far agrees with me in stating that “ typical phloem, consisting 
of delicate elongated elements, cannot always be recognised, even 
in the best-preserved specimens .” 3 
The position for which I have contended may prove to be 
untenable, but the facts at present available appear to me to support 
the opinions already expressed, viz. (1) Lepidodendron did not possess 
a cambium-layer of the same type as that of most recent plants, 
( 2 ) that the tissue, which from its position might be designated 
phloem, did not exhibit the characters usually met w r ith in that 
tissue, and (3), that the formation of secondary stelar tissue was 
chiefly, if not entirely, confined to the secondary xylem. 
The nature of the tissues in Lepidodendron which corresponded 
to the cambium and phloem of recent plants is by no means 
definitely settled; and my object in writing these notes is not 
merely to justify my previous statements, but to call the attention 
of those interested in the study of fossil plants to some of the 
anatomical and physiological questions on which further information 
is needed. 
1 Scott, 1900. P. 142. 
2 Jeffrey, 1897. “ The Gametopliyte of Botrychium Virginianum. 
Traus. Canad. Instil., vol. v., pt. ii., p. 284. 
3 Scott, loc. cit. p. 142 . 
