4 ^ 
A. C. Seward. 
parenchymatous elements form the greater part of the secondary 
wood) by several layers of cells. In other words, the region which 
is designated cambium is rather further away from the mature 
secondary xylem than it is in recent plants. The conclusion is, that 
I was mistaken in considering the disorganisation of the tissue, 
which I called the secretory zone, as connected with a secretory 
function, the resemblance to secretory groups being due to 
post-mortem changes in a zone of ordinary phloem. The more 
compact nature of the extra-cambial zone in the Manchester 
specimens may indicate that the tissue in question was not secretory, 
but in the absence of evidence furnished by longitudinal sections we 
cannot arrive at any satisfactory conclusion as to histological 
characters. It is a pity, as Professor Weiss says, that there are no 
longitudinal sections of the specimen; they alone can decide whether 
the groups of cells compared by him to sieve-tubes surrounded by 
companion-cells are of that nature, or if they are of the nature of 
short and delicate cells which would eventually become disorganised, 
leaving the oval spaces which usually characterise the ‘ phloem ’ 
regions in Lepidodendron. The clusters of so-called sieve-tubes 
and companion-cells are no doubt identical with those represented 
in fig. 3 1 of my description of the same species, and spoken of as 
“ small elements enclosed by a thin oval membranethey are also 
indicated in some of the large vertical spaces represented in fig. 5 
of the same paper 2 . The evidence at present available does not 
appear to me to support Professor Weiss’ conclusion; it believe that 
these cell-groups are most probably preserved in the Binney sections 
as they existed during life; the fact that they are less disorganised 
in the Cash specimen of Lepidodendron does not afford proof that 
they did not possess a secretory function. We, have, in short, no 
satisfactory evidence of the sieve-tube nature of any of the 
elements in the tissue which Weiss describes as phloem. I do not 
wish to overlook the possibility that the features which led me to 
make use of the term secretory zone may be found to have been 
unsafe guides, and that they may afford another instance of the 
difficulty of distinguishing between original and secondary structures. 
It may be as Professor Weiss 3 has suggested, that the chemical and 
physical constitution of the walls of the elements of the extra- 
cambial tissue may have been such as to favour mucilaginous 
1 Seward, 1899. P. 147. 
2 Ibid. P. 151. 
3 Weiss, 1901. Pp. 13 et seg. 
