Bancroft.—On the Xylem Elements of the Pteridophyta. 747 
sections, he has been able to demonstrate that the pit-membranes are 
typically present in the end, as well as in the lateral walls of the elements. 
(In Pteris Aquilina the pit-membranes disappear from the cross walls, these 
being much less inclined to the lateral walls than is usual.) Halft further 
demonstrates that the primary wall remains between the bars of secondary 
thickening. The difference in the amount of cohesion of the bars gives rise 
to the presence or absence of the £ split * between them, as seen in transverse 
section. 
The results obtained by the writer lend strong support to the views put 
forward by Halft with regard to the tracheidal nature of the xylem elements 
of the majority, at least, of the Pteridophyta. 
B. Methods and Material. 
Unstained transverse sections of certain types, e. g. Gleichenia spp., 
Lygodium spp., and others, gave the impression that true empty spaces 
occurred between contiguous elements of the xylem, as Gwynne-Vaughan 
maintains. These sections when stained, however, failed to confirm the 
idea, the spaces never appearing clear, even under a magnification of 
325 diameters. 1 The appearance of Halft’s paper suggested the reason for 
this and led to the following investigations. 
I. Microchemical Tests for Pec tic Substances of the Primary Walls . 
Several chemical methods were employed in order to prove the presence 
of primary pectic substances separating the secondary lignified layers of 
the xylem elements. The first of these methods was that mentioned by 
Halft ( 3 ). This investigator treated transverse sections of Pteris Aquilina 
and Osmunda regalis with Schulze’s maceration mixture (concentrated 
nitric acid and potassium chlorate), until the lignin of the secondary layers 
of thickening had disappeared, but apparently before the stronger lignifica- 
tion of the primary walls of the elements had been destroyed. It is a well- 
known fact that lignified walls, after treatment with this maceration fluid, 
give the cellulose reaction. Halft therefore removed the residue of cellu¬ 
lose from his sections by means of strong sulphuric acid, and found that in 
the cases mentioned the primary walls and pit-membranes remained as 
a delicate network on the slide (cf. Strasburger, 17 ). In his description 
of the method he remarks that if the maceration fluid had not acted for 
a sufficient time the middle substances were much swollen, and that after 
treatment with H 2 S 0 4 they showed as a deep brown line, the secondary 
layers of thickening not disappearing entirely. If, on the other hand, the 
macerating medium had acted for too long a time the primary wall vanished 
along with the secondary layers on the addition of H 2 S 0 4 . 
1 Swift’s 1/6 objective. No. 3, ocular. 
