Boodle.— Anatomy of the Schizaeaceae . 399 
but that the whole protoplasm of the sieve-tubes is connected, 
and represents it so, e. g. in his Fig. 2 6. Poirault (’ 93 , p. 138) 
found callus blocking the pores of the sieve-plates generally 
in the Ferns, though absent in Ophioglosseae and Marattiaceae. 
He points out (p. 139) that Terletzki had confused under the 
same name ( £ very refractive bodies adhering strongly to the 
wall ’) the proteid granules and the callus stoppers. Poirault 
found that azo-violet left the former uncoloured, but stained 
the latter bright pink. 
The results obtained with azo-blue correspond on the 
whole with those of Poirault, in that callus was found in 
Thyrsopteris, in Dicksonia and in several of the Polypodiaceae, 
but not in Ophioglossum nor in Marattiaceae. However, callus 
was not found in Schizaeaceae nor in Hymenophyllaceae, 
though these Orders are not cited by Poirault as exceptions 
to his generalization. 
In Pteris and in Thyrsopteris , where the callus was specially 
well developed, it took the form of a small rod running through 
the pore, and often e. g. on the vertical walls expanded into 
a round knob at each end. The knob was frequently sur- 
rounded by a perfectly neat ring of refractive granules. This 
structure corresponds with Russow’s description, but De Bary 
(’ 77 , p. 181 and accompanying figure) did not distinguish 
between the refractive granules and the callus-knobs, and 
evidently saw the callus-rods but apparently took them for 
protoplasmic connexions, as Terletzki also seems to have 
done. Callus-rods are also found in the pits connecting sieve- 
tubes with phloem-parenchyma-cells. 
Poirault (’ 93 , p. 138) states that callus is formed very early 
on the pores of the sieve-plates, and the callus, when formed, 
appears to completely fill the pores ; so it seems that in Pteris 
aquilina and many other Ferns the sieve-tubes have no 
protoplasmic connexions through the sieve-plates, except 
perhaps at an early stage. But there is the possibility 
that there may be a delicate protoplasmic thread running 
through the callus-rod and only recognizable by more refined 
methods. 
