88 BOTANICAL GAZETTE [JANUARY 
should be pointed out that on the basis of the first alternative 
the transitions between multiseriate and scalariform pitting are to 
be interpreted in the reverse direction, the multiseriate pits having 
been derived from the scalariform. 
But, no matter which of these two views is the correct one, it is 
plain that the vessel with the scalariform end wall is the primitive 
) kind in angiosperms. One evi- 
dence that this is true is the fact 
that it prevails in those angio- 
sperms which are admittedly 
primitive, whereas the type with 
the single large perforation pre- 
vails in the higher forms. Some- 
times the two types are found in 
different members of the same 
family, but in such cases the more 
primitive members of the family 
are characterized by the posses- 
ANNO 
) 
sion of the scalariform type, while 
the higher members have the 
singly perforated type. 
a é S That the scalariform type of 
Fic. 11.—Series of vessels from vessel is the primitive one is 
wood of ol poms zie wi further shown by cases of actual 
eaite: stent ints se ee transformation of this kind into 
perforation. the kind with the single perfora- 
tion. Not only do these cases 
prove the primitiveness of the former, but they also give us a 
picture of the evolution of the single perforation. 
Some years ago the writer discovered in the wood of Vaccinium 
all transitions between the scalariform perforations and the single 
large perforation. The process consists simply of the gradual loss 
of the bars. Some stages are represented in fig. 11. A typical 
scalariform vessel is shown in a; in b two bars remain intact, two 
more are incomplete, and the positions of others are indicated by 
the projections from the sides. Random samples further illustrat- 
ing the process are represented inc and d. In/ the process is nearly 
