JuLy 5, 1918] 
plete transformation into typically perforated 
scalariform vessels. 
It is evident that, to the extent that ad- 
jacent cells become specialized, and unlike in 
shape, in size, and in function, as, for ex- 
ample, the tracheal segment and an adjacent 
prosenchyma cell of the angiosperms, the 
sealariform pit must lose its alignment as an 
intercommunicating structure. Conversely, the 
circular pit is the more adaptable, and prevails 
in the vascular elements of more advanced 
plant families as typified by the Composite. 
Just as might be hypothesized, the scalariform 
pit is relatively more common in the vascular 
elements of less specialized families included 
in the Ranales. Probably the scalariform pit 
prevailed in the early angiosperms, and is 
even now being slowly discarded for the smal- 
ler circular pit. It was, in case of the vessels, 
first discarded on the lateral sides adjacent 
specializing tracheids, ray-cells, wood-paren- 
ehyma, or, especially, fibro-tracheids and fibers. 
The close relation between a vessel and the ad- 
jacent element or elements is evident from the 
fact that, for example, in Cheirodendron (Ara- 
liaceew) four distinct types of pits communi- 
cate respectively with prosenchyma, wood-paren- 
echyma, ray-parenchyma, and with other ves- 
sels. However, that the end-walls should pre- 
serve the more primitive sculpture is quite in 
harmony with the fact that adjacent cells 
are, in this case, alike. Complex modification 
is here unnecessary, and adequate comparisons 
of the secondary wood of existing primitive 
and specialized families proves the correctness 
of the view advanced. It is indeed a remark- 
able fact that in woods with scalariform per- 
forations in the vessels, the prosenchyma usu- 
ally bears distinctly bordered pits and is thus 
less distinct from the tracheal segment than 
in case of woods in which the vessels are 
characterized by the simple or porous perfor- 
ations. 
A feature of interest not mentioned by Jef- 
frey is the more or less frequent occurrence of 
branched bars. They occur occasionally in 
Liriodendron and other genera with scalari- 
form perforations; but in Cheirodendron and 
some other araliaceous woods this branching 
SCIENCE 17 
of the bars in the perforation may become 
more or less intricate. 
Comparison of such types with the scalari- 
form wood of Cycadeoidea Dartoni has been 
suggested by Dr. Wieland, and for the purpose 
he has placed before me recently cut sections. 
The preservation of this fossil is perfect. The 
sections show the minutest detail in the pit- 
ting of the tracheids, even under a magnifi- 
cation of 450 diameters. The outline of the 
pits, the pit-apertures, and other minute char- 
acters are preserved in every detail. The 
sides and ends of these tracheids, in both 
tangential and radial aspects, are pitted with 
regular scalariform bordered pits, which at 
once remind one of those of Magnolia. Along 
with the true scalariform pits occur a few 
elliptical pits, and these are inserted between 
the long pits in such a manner that, by the 
dissolution of the borders and closing mem- 
branes, occasional branched bars would result. 
The resemblance between the pitting of these 
cycadeoidean tracheids and the vascular ele- 
ments of Magnolia on the one hand, and 
of Dracena on the other, is perfect, and may be 
followed out in minute detail. 
The evidence in support of the hypothesis 
that scalariform pitting is primitive is con- 
vineing. It is evident that the process of the 
breaking up of scalariform pits into circular 
pits was in progress in the antecedent cycads, 
and that this process started first in the tra- 
cheid side-walls, whereby the overlapping tra- 
cheid ends became more conservative than 
their truly lateral portions. The complement- 
ary relations in the wood of the cycadeoids 
and eycads outlined in Wieland’s recent note* 
are thus anatomically reconciled. The origin 
of branched bars is also explained. 
Excellent examples to show that perfect 
scalariform tracheids exist in living types 
occur in Magnolia hypoleuca. The scealari- 
form pitting very closely approximates that 
of Cycadeoidea Dartont. Scalariform tra- 
cheids slightly more advanced may be found 
in the aquifoliaceous Byronia sandwicensis 
Endl. Here the tracheids retain typical sca- 
1 Wieland, G. R., Feb., 1918, ‘‘Cyeadoid Wood 
Structure,’’ Science, N. S., XLVII., pp. 141, 142. 
