C. A. BARBER. Pai 
region separate to isolated rows (Sant. IJ, Plate VI, fig. 2, a, a). 
They are here separated by thin-walled, small-coated paren- 
chyma (Plate VII). A curious circumstance about this inter- 
rupted zone is its extremely early appearance, some of the first 
stages of vascular development met with showing complete 
disorganisation at this point and, presumably, a complete 
dislocation of the vascular system. In other cases, however, 
it has been observed that the outermost strands are still normal 
while the inner ones are yellowed. The yellowing is centri- 
fugal, and passes outwards in much the same manner as the 
duramen in the secondary wood, only it is much more rapidly 
completed. In the figures on Plate VII these points are illus- 
trated. In the first two figures yellowing is complete, mere 
traces of pitting alone being found on the outermost row 
of vessels. In figure 3, however, the outer row is apparently 
still intact, while all the rest are filled with gummy substance. 
It should be noted that the last mentioned case is not very 
common and the appearance shown in figures 1 and 2 is more 
usual. 
As already remarked (Sant. II, para. 9), it 1s difficult to 
understand the utility of this arrangement, for it would appear 
that interruption occurs very shortly after the sucker has 
reached the woody cylinder of the host and soon after the 
fusion of the vascular systems of the two plants. The conclu- 
sion at present arrived at is that the activity of the haustorium 
is extremely short and that, as in ordinary plants, the absorbing 
portion of the root-system in these parasites functions only for 
a short time, and this absorbing power is passed onwards as 
the roots grow in length, branch and encounter new foreign 
systems to which to attach themselves. According to this 
view, the parasite is brought into contact with new roots in 
rapid succession and the old suckers are practicaliy closed. If 
this be true, on the other hand, it is difficult to understand the 
amount of secondary thickening which takes place in some 
haustoria, the new vessels being apparently closed in succes- 
sion almost as fast as they are formed (Plate IX, fig. 5). 
