Notes. 
1 23 
is easy to imagine that a ligule may have been developed in the 
Filicinae as it has been in the Lycopodinae, to say nothing of other 
groups of plants. 
On summing up the evidence, it appears to be proved that there 
is quite as much resemblance between Isoetes and the Eusporangiate 
Filices, as there is between Selaginella and the Lycopodiaceae ; and 
further, that there is a closer resemblance between Isoetes and the 
Eusporangiate Filices than there is between Isoetes and the recognised 
Lycopodinae. At the same time, it must be admitted that there is 
some affinity between Isoetes and the Lycopodinae. But it has long 
been recognised that the Eusporangiate Filices are those Filices which 
have most affinity with the Lycopodinae ; and, in uniting Isoetes with 
the former group, this affinity merely becomes more marked. 
In conclusion, I would point out that the proposed change in the 
systematic position of Isoetes throws an altogether new light on the 
evolution of the Phanerogams from the Pteridophyta, but I reserve 
the discussion of this question for a future occasion. 
S. H. VINES. 
PRELIMINARY NOTE ON THE DEVELOPMENT OF 
THE ROOT OF EQUISETUM. — I undertook, as the result of 
some discussion with, and at the suggestion of, my friends Dr. Vines 
and Mr. Gardiner, to determine the somewhat doubtful point of the 
development of the double endodermis of the root of Equisetum. As 
I have not, at present, time to prepare a full account of my investi- 
gations I propose to give in this note the main results obtained. * 
The apical cell of the root gives rise to two kinds of tissue which 
can at once be distinguished from one another by the sequence of 
divisions. Of these, one forms an outer layer or cylinder constituting 
the exomeristem of Russow; the other is enclosed by it forming a 
central cord of tissue constituting the endomeristem of the same 
author. 
The exomeristem is distinguished from first to last by its cells being 
arranged in radial rows, most distinctly so in the zone of cells 
immediately surrounding the endomeristem. The endomeristem may 
be said to be chiefly distinguishable by the fact that its cells are not 
arranged in radial rows, and are also smaller than the cells of the 
exomeristem. No one can possibly fail to see at the first glance 
where the line passes separating the two meristems. This is especially 
