2 IO 
D. ft. S. 
stelic type may arise by reduction from an amphiphloic siphonostele. 
This is an important step, but it by no means proves that the theory 
holds good generally. To take an analogous case; an apparently 
protostelic structure is known to have arisen in certain cases 
( e.g . water-plants) by reduction, yet no one doubts that in other 
groups the protostele is really primitive. 
The author’s treatment of the Lycopodiales is somewhat 
meagre. The first type described is a highly complicated Selaginella, 
S. laevigata, with a tubular amphiphloic stele, and accessory medullary 
strands, the “ ramular gaps” here replacing the leaf-gaps of the 
Ferns. This species was regarded by Harvey-Gibson as relatively 
primitive on account of the tubular form of stele, recalling that of 
many Palaeozoic Lepidodendreae. The resemblance, however, is 
superficial, for in none of the fossil Lycopods is any tissue present 
which could be interpreted as internal phloem. On the contrary, 
the whole of the extensive fossil evidence supports the direct 
derivation of the medullate stele, so far as it occurs in Lycopods, 
from protostelic structure, Whatever may be the case with other 
groups, it would scarcely seem admissible to apply the author’s 
theory of reduction to the Lycopodiales. 
We next come to the Gymnosperms, under which head the 
extinct Cycadofilices are considered In the genus Lyginodendron, 
of whieh the anatomy is pretty completely known, the author 
regards the pith as forming part of the ground-tissue, and, what is 
more important, believes that the collateral bundles of the stem 
have arisen by reduction from a system of concentric strands. 
In support of the former position he states that similar clusters of 
sclerotic cells occur in both medulla and cortex. In the internodes, 
however, it is in the pericycle , not in the cortex, that they are found, 
though at the nodes and in the petiole they become cortical. 
In fact these nests occur in all regions, and have no bearing on the 
homologies of the tissues. As evidence of reduction from concentric 
structure Professor Jeffrey relies on “the occasional occurrence of 
concentric bundles in the stelar tube.” It must be pointed out, 
however, that the inverted wood and bast, which render the bundles 
“ concentric ” in these exceptional cases, appear to be entirely of 
secondary origin; they thus form an example of “ anomalous 
secondary thickening ” in the sense of De Bary, and afford no 
evidence of any variation in the primary structure. It is a pity 
that this fundamental objection to his interpretation is not dealt 
with by the author. 
