1921] MACDUFFIE—VESSELS 441 
high magnification of a vessel in Alnus japonica, in which the origin 
of the scalariform perforation from fusions of rows of pits is clear 
and convincing. 
We pass now from woody Angiosperms to the consideration of 
the herbs and vines among Angiosperms, which in their vascular 
structures more closely resemble the conditions found in Guetum, 
and show stages of perforation strikingly like those found in that 
genus. Fig. ro is a section through the wood near the pith of 
Potentilla palustris. Several vessels are shown in the figure with 
a rather advanced development of the scalariform pits in the region 
_ Of perforation. This condition resembles that found in the mature 
wood of Almus. Fig. 11 is a section taken from the medullary 
region of Potentilla monspeliensis, an annual species. To the left 
are the characteristic spiral and scalariform tracheids of the 
protoxylem, and to the right are vessels with scalariform perfora- 
tions on the end wall. Of these vessels, the one to the right shows 
a tendency at its lower end toward fusion of the scalariform pits. 
To the extreme right of the same figure is a vessel, low in the field, 
with the single large bordered pore characteristic of the mature 
wood of Potentilla as well as of the vessels of Gnetum. <A further 
example of the close relation to the Gnetalean pitting is found in 
fig. 12, another section of the wood of Potentilia mons peliensis. 
To the left are two vessels in series. Both have the small pits 
grouped for fusion as in Ephedra and in certain species of Gnetum 
(figs. 1-3); in fact several of the pits have already fused in the 
higher vessel. To the extreme right is a vessel with a large Gnetum- 
like pore. Fig. 13, another section of Potentilla monspeliensis, 
shows three other vessels in the region of perforation. The vascular 
element to the left has again Ephedra-like pits grouped and fusing. 
The two vessels to the right in series have a curious S-shaped fusion 
of pits, quite out of keeping with any mode of origin save a 
haphazard union of pits. Fig. 14 shows part of the same field 
under higher magnification. It is clear that the two vessels here 
manifest the process of fusion of numbers of small pits. Fig. 15 
is a high magnification of a similar condition in the same genus. 
Examples of like conditions might be indefinitely multiplied from 
