577 
Sieve-Tubes of Pinus . 
Russow’s paper on the development of sieve-tubes 1 2 was 
published shortly after Janczewski’s, and shows a great advance 
in knowledge and methods of observation, but it is most 
unfortunately marred by a total absence of illustration. The 
omission to append figures to a paper is a great drawback, 
especially when it deals with questions of minute histology ; 
and no doubt this accounts for the fact that Professor 
Russow’s remarkable papers have not met with the recogni- 
tion they deserve. 
In the paper under consideration Russow first describes the 
structure of the cell-wall of Gymnospermous sieve-tubes, and 
then confirms De Bary’s results on the sieve-plate, pointing 
out that the sieve is divided up into irregular fields, each of 
which is perforated by three to six little holes of fairly 
different diameter, usually arranged in a circle (Fig. i, 
PI. XXXI). Russow worked mainly with his ‘ callus reagent Y 
which, while it gives excellent staining with callus, stains the 
protoplasm also, so that it is very hard to differentiate the 
one from the other. It seems chiefly owing to this property 
of the reagent that so much confusion exists as to the relation 
between protoplasm and callus in the sieve-plate of Gymno- 
sperms ; from what follows it will be seen that Russow, like 
later writers, was at first misled with regard to the callus. 
In a transverse section of the sieve-tubes, he found that the 
mature radial walls are traversed by red-brown rods, swollen 
at the head (geknopften Stdben ) and interrupted at the middle 
lamella by nodules usually coloured yellow (Figs. 3, 4, arid 5, 
PI. XXXI, gs. mi). Each half of a rod is spoken of as a 
callus-cork (Fig. 5, PI. XXXI). 
The sides of the callus-corks ( Callus-Pfropfen ) have a dark 
edge or appear enclosed by dark brown striae, which he 
regards as being identical with the striae found traversing the 
callus- cushions of Angiosperms. These he calls the callus- 
1 Russow, Sitzber. der Dorpater Nat.-Ges., 1882, p. 264; trans., Ann. des Sc. 
Nat., Bot., 6° ser., tome xiv, 1882, p. 173. 
2 Russow’s callus reagent, a mixture of equal parts of chlor. zinc, iodine and 
a solution of iodine in potassium iodide. 
