‘ Sanids Bars ’ in Pinus Inops. 
42 1 
fill the whole lumen of the tracheide, i. e. be a complete transverse wall ; and 
it is difficult to explain their occurrence in radial rows at the same height 
in the cambium cell, as the protoplasm is constantly streaming. The strand 
of protoplasm would therefore be stationary, and further the vertical radial 
plate-like nature of the bars is not possible on this hypothesis. Muller 
alleges that the bar form, stretching from wall to wall, is not shown in the 
cambium cell ; the bars are free at both ends. (As will be shown later, this 
statement is not correct.) 
2. In support of Muller’s second possible mode of origin, that the bars 
are produced by partial reabsorption of the transverse tracheide walls, he 
stated that the presence of square ends to tracheides is not uncommon in 
Ginkgo\ in some cases rows of tracheides occur, each tracheide having 
a square end wall. Against this view, however, Muller points out that 
square end wails are rather the exception than the rule, and that a partial 
solution of transverse walls is otherwise not known in coniferous wood ; and 
he further points out that if reabsorption took place in tangential sections 
the bars would appear elongated in the transverse direction, whereas they 
are elongated in the long direction of the tracheide. 
3. In support of his third suggestion, that the bars are formed by 
folding of the tangential tracheide walls, he points out the infolding of the 
cell-walls in the mesophyll of Pine leaves, also the folding of the walls of 
transfusion tissue and the occasional folding over of a tracheide when it 
comes in contact with a medullary ray. 
The view finally adopted by Mtiller is : 
‘ Sanio’s bars ’ arise from folds of the radial walls of the cambium cells, 
and the transition from plate to bar form depends on partial reabsorption, 
which results in the setting free of the bar as a consequence of the total 
reabsorption of the bar groundwork in the cambium cell. 
In 1892 W. Raatz ( 7 ), working independently at the same time as 
Muller, published at a later date his observations on ‘ Sanio’s bars ’, and 
added to the list of species in which the bars occur, including the xylem of 
the veins of the leaves of Hippophae rhamnoides , root, stem, and secondary 
wood of Salix fragilis y and Casuarina equisetifolia . Raatz pointed out 
that the bars are not universal phenomena and not structures to be relied 
on as always occurring, and further stated that in Abies pec tinata frequently 
little projections occur on the middle of the bar. 
Raatz summarizes the development of the bars in the following way : 
1. The bars are more or less abnormalities, not arising in any regular 
order and not having any definite function. 
2. The bars are formed by the tangential walls of the cambium cell 
coming in contact, and as this cambium cell gives rise to a tracheide and 
the walls become lignified, so the walls of this bar becomes lignified. 
From the various theories as to the origin of ‘ Sanio’s bars ’ and the 
