the Sieve- tubes in Laminar ieae . ioi 
and development of these ducts in this and allied genera 
would form the subject of an interesting account, but I do not 
propose to follow the subject further here. 
If longitudinal sections through the medulla of an adult 
stem be examined after being mounted in corallin-soda, 
numbers of large trumpet-hyphae will be seen. These are 
rendered extremely conspicuous from their being full of 
callus which stains an intense rose-pink. The larger ones — 
of which one is represented in Fig. 5 — attain to a diameter of 
•056 mm. These occur with great frequency, and almost 
always have the characteristic form represented. The walls 
are often very thick, and the sieve-plates show fairly large 
perforations, though not so wide as in the true sieve-tubes. 
The wide part of the tube on either side of the sieve-plate is 
filled up with callus which can be traced a short distance along 
the inner layers of the wall in the narrowed portion of the 
tube. The shading off of the pink colour in Fig. 5 shows how 
far the callous change has extended. 
In Fig. 9 is shown a formation of callus of somewhat excep- 
tional character, though none the less valuable in pointing to 
the mode of origin of the callus. The lower portion of the 
figure represents the end of the callus-plug, c.p., in such a 
trumpet-hypha as is given in Fig. 5. The callus, as is shown, 
has been formed by the alteration of the inner layers of the 
cell-wall. In one of the layers, however, the callus-formation 
has not been confined to the widened part of the trumpet- 
hypha, but a local callus-formation at /. c. has taken place. 
The layers of the wall both inside and outside this one do 
not in any way participate in this local change, and the in- 
most layer is considerably displaced owing to the increase in 
bulk accompanying the callus-formation. The lumen of the 
tube /. is represented black ; it has been caused to deviate 
from its original straight course by this anomalous develop- 
ment. This particular case lends, I think, strong support to 
the view that in the trumpet-hyphae, at any rate, the callus 
is formed directly from the cell-wall. This should be com- 
pared with Fig. 10, described on page 105. Besides the type 
