748 Bancroft.—On the Xylem Elements of the Pteridophyta. 
Halft’s method was followed in the treatment of sections of the petioles 
of Marattia elegans and M. laxa , but the results seemed to indicate that 
the mature tissues used were too strongly lignified for the maceration fluid 
to remove the lignin completely before the dissolution of the lamella took 
place. Other experiments, however, were decidedly satisfactory, sections of 
Selaginella Wildenovii , treated for a very short time with the maceration 
fluid and then transferred to strong H 2 S 0 4 , giving the desired result. The 
primary membranes remained after the removal of the secondary layers, but 
at the corners of the cells small patches of lignified substance also remained, 
demonstrating that these were the most strongly lignified areas, and there¬ 
fore the most resistant to the macerating fluid (cf. Text-fig. 1). 
Text-fig. i. Part of a transverse section of Selaginella Wildenovii after treatment with 
Schulze’s maceration fluid and H 2 S 0 4 , showing the primary wall and the patches of lignified 
substance. 
A further microchemical test giving uniformly good results was used. 
Thin sections of Marattia spp. and Gleichenia circinata were stained with 
methylene blue, the lignified walls of the xylem elements taking on a bright 
blue colour. Between the lignified bars was a substance which stained 
violet-blue, this indicating its pectic character (Stevens, 15 ). On mounting 
in glycerine the violet-blue of the middle substance faded rapidly, while the 
bright blue of the lignified parts remained unchanged. The decolorization 
in glycerine is a further characteristic of pectic substances when stained with 
methylene blue (Mangin, 7 - 9 ). 
Following Mangin’s method, thin sections of Selaginella Wildenovii 
were treated for twenty-four hours with acid-alcohol (one part of acid 
to five of alcohol), then thoroughly washed with distilled water, and stained 
with methylene blue. In this case also the primary parts were differentiated 
(Mangin, 7 - 9 ). 
It will thus be seen that the microchemical evidence for the presence of 
a primary membrane is decidedly convincing. 
II. Physical Methods of Testing the Nature of the Xylem Elements. 
The methods used by Halft were not repeated, but one of his experi¬ 
ments was utilized in a somewhat modified form. 
Portions of the petioles of Marattia spp., Angiopteris evecta, and several 
polypodiaceous types, and also pieces of the stems of Selaginella Wildenovii 
and Psilotum triquetrum , were injected (by means of an air-pump) with 
water containing in suspension a considerable amount of finely ground 
