108 Z. A. Boodle 
other leaf. In the case of the stem of a typical Dicotyledon, in 
which all the primary bundles are leaf-traces, the above method of 
description is no doubt the most convenient. 
When one is dealing with certain ferns, which have a solid 
cauline stele, or in which there are no leaf-traces showing distinct 
individuality in the internode, often the easiest method of description 
is one, which starts with the internodal structure of the stele and 
follows the acropetal direction to the node; in this way it is clearly 
seen what part of the stele is continuous with the leaf-trace. The 
acropetal order has been largely followed in recent papers on ferns, 
when the authors have been dealing with the structure of the 
mature stem, and is naturally adopted in the fern-seedling, when 
the object is to trace the gradually increasing complexity in the 
arrangement of the vascular tissues of the stem as shown by the 
ontogeny. 
In many cases, according as one describes the vascular and 
other tissues as traced upwards or downwards, one is easily led to 
use phrases, which commit one to a different opinion as to their 
morphological nature in the two cases. To take an example, in 
certain species of Gleichenia, e.g. G. flabellata 1 the internodal 
structure shows a stele with a central solid mass of xylem (i.e. a 
protostele); as one approaches the node from below, a strand of 
sclerotic tissue appears in the xylem-, but, at the node, becomes 
connected with the sclerotic tissue of the cortex, during the 
separation of the leaf-trace. Firstly, adopting the acropetal order, 
one states that a strand of sclerotic tissue appears in the xylem of 
the stele and becomes continuous with the cortex at the node. 
Secondly, the opposite treatment is to describe a strand of 
sclerotic cortex as penetrating the stele at the node and passing 
downwards for a short distance within the stele. According to the 
method pursued one is led to regard this strand as belonging to the 
stele in the one case and to the cortex in the other. 
As a second example we will now take the young sporophyte of 
a fern, such as Anemia Pliyllitidis , the mature stem of which is 
dictyostelic 3 , that is to say its vascular tissue forms a tubular 
network of concentric vascular strands. The lower part of the 
seedling-stem has a simple stele containing a centrally placed solid 
core of xylem. In passing upwards, the middle part of the xylem 
’• See Poirault, Kecherclies sur les Ciyp. Vase., Ann. des Sci. Nat., 
Hot, 7 ser , tom. xviii., p. 177, Fig. 17 and Hoodie, Anatomy of tlie 
Gleicheniaceae, Annals of Botany, vol. xv., p. 1-23. 
2 Further details are omitted for the sake of clearness. 
3 Brebner, Anatomy of Danaea, etc., Annals of Botany, vol. 
xvi.,p, 523. 
