400 Boodle. — Anatomy of the Schizaeaceae . 
Fibres. 
Fibrous elements, as described above, occur in the petiolar 
bundle of certain species of Lygodium , Anemia , and Sckizaea, 
but are absent in Mohria. In all three genera they appear 
to represent thickened and lignified sieve-tubes. In Gwynne- 
Vaughan’s interesting paper on Loxsoma (’ 01 , p. 83, &c.) 
similar fibres are carefully described in that genus, and their 
nature in that and other cases discussed. The conclusion he 
arrives at is that in Loxsoma the fibres represent elements 
of the phloem originally designed for sieve-tubes, and he 
extends the same explanation to the fibres of Lygodiitm , 
Schizaea , and Anemia. The position and structure of the 
fibres in these three Schizaeaceous genera entirely support 
this view, and further in Lygodium lanceolatum and in Anemia 
Phyllitidis some of the fibrous elements may have even 
functioned as sieve-tubes prior to their sclerosis. This is 
suggested by the presence of granules on the end-wall of 
Fig. 19, and by the late sclerosis of some of the large sieve- 
tubes in the species of Lygodium just mentioned. In the case 
of Trichomanes Prietirii , as pointed out by Gwynne- Vaughan 
(’01, p. 86), all the sclerotic elements cannot be regarded as 
derived from sieve-tubes, as the end-walls of some of them do 
not at all resemble sieve-plates. Others however, judged by 
their structure, might represent sieve-tubes, as in the element 
shown in Fig. 46. No granules were observed on such end- 
walls, and it must be remarked that structures almost identical 
with the example figured may be met with in other sclerotic 
tissues, for instance in the epidermis of a rather old petiole of 
Mohria caffrorum. Hence it is necessary to depend more on 
the position of these elements in T. Prieurii for an explanation 
of their nature. This was chiefly relied on in the paper on the 
Hymenophyllaceae (Boodle, ’00, p. 4 75), where the fibres were 
regarded as being derived from parenchyma. This still 
appears extremely probable for the bulk of the fibres, but 
it must be left doubtful whether some of them may have 
been derived from sieve-tubes. Some of the fibres lie 
