390 Farmer and Hill. — Arrangement and Structure 
with the bases of these organs. In the latter they form a 
circle around the stele, and the cells containing the secretion 
are apparent at a very early age. The presence of the tannin 
seems to be associated with a suppression of cell divisions, for 
the individual cells grow to a great length as the organ as 
a whole increases in size. They often form chains of cells 
which are continuous for a considerable distance, and in some 
cases at least we have found evidence that the cross walls 
separating two adjacent cells may break down 1 . 
The mucilage ducts, which are, unlike the tannin cells, 
chiefly confined to the stems in young plants, commonly make 
their first appearance within the pith, or horse-shoe shaped 
area of parenchyma which is formed when the continuity of 
the vascular cylinder is interrupted owing to the departure 
of the leaf-trace. At first, in the parenchyma exposed by the 
foliar gap, a mucilage duct is formed, and it dies away above, 
when the level is reached at which the gap is closed. Fre- 
quently, however, it branches below this, and one of the two 
limbs accompanies the leaf-trace for a short distance before 
ending blindly. The subsequently formed ducts may traverse 
a longer interval before ending blindly, but all of them, so far 
as the study of young sporophytes serves to illustrate them, 
are isolated and of no great length ; they all divide before 
ending blindly, one of the arms passing out with the leaf-trace 
strand. They all arise lysigenously, as was stated by Kuhn, 
at any rate in the young plants ; we were not able to find any 
instances which admitted of explanation as having arisen 
schizogenously. Brebner 2 has described a schizogenous 
origin for those studied by him in species of Marattia and 
Angiopteris , and Lutz 3 states that their origin may be either 
schizogenous or lysigenous. The only instances we saw which 
could give rise to the appearance of schizogeny always proved 
to belong to the extreme upper ends of the lysigenous ducts. 
It would thus appear that at any rate the lysigenous origin is 
characteristic of the stems of the young plants, and therefore 
1 Cfi Farmer* loc. cit. • 3 Journ. Linn. Soc., xxx. 
8 Journ, de Botanique, xii, p. 135. 
