ORR—TRACHEAL TISSUE IN CAPPARIDACEAE. 253 
and the extent of the thickening of the tracheid walls is by 
no means uniform. It is therefore possible to classify them 
artificially for purposes of description on the basis of these 
minute structural differences. 
1. The tracheal envelopes of Capparis decidua, Pax (aphylla, 
Roth), and Capparis spinosa, Linn., are composed of isodia- 
metric cells with relatively deep anticlinal walls. In the case 
of Capparis decidua the anticlinal walls are closely reticulated, 
while in Capparis spinosa the thickening is more of a spiral 
conformation. Owing to the depth of the tracheides these 
anticlinal walls are easily seen in surface view, and the two 
types are readily distinguishable. 
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I 
Fic. 2.—(1) A portion of the tracheal envelope of Capparis decidua, Pax, in 
surface view. (2) Diagrammatic drawing ofan isolated tracheid. x about 350. 
In the remainder of the species the tracheal elements are 
much shallower, and the nature of the thickening cannot be 
so readily observed, nor does it appear to be uniform in the 
cells of any one species. In the portions of the tracheal enve- 
lopes which have been figured, the thickened lateral walls are 
shown as if in section, which is the most characteristic appear- 
ance presented by these sheaths in surface view. The irregular 
configuration distinguishes them definitely from the two species 
just described, and in some cases it more closely approximates 
to the type of structure found in allied genera. This diversity 
of sheath character within the limits of the genus is suggestive 
of its composite character. 
2. Of the species possessing shallow tracheides, Capparis 
micracantha, DC., most closely resembles Capparis decidua. 
The tracheides are approximately the same size in surface view, 
but are of the shallow type, while the thickening is not so definite. 
The spirals on the lateral walls are broad bands, but in some 
elements they assume the form of a network. A somewhat 
