ORR—TRACHEAL TISSUE IN .CAPPARIDACEAE. 251 
1. Cleomeae. 
The three genera examined were .Cleome, Linn., Isomeris, 
Nutt., and Polanisia, Rafin., and, as might be expected, their 
natural affinities are further emphasised by the similarity of 
structure found in the tracheal envelopes of their seeds, In the 
species examined, the tracheides are parenchymatous cells with 
delicate annular thickenings on their periclinal or surface walls, 
a feature which, so far as can be ascertained, is peculiar to the 
Cleomeae. 
In many of the cells these fine bands of thickening are laid 
down in two, or even three, distinct concentric zones; and in 
Fic, 1.—A portion of the tracheal — of (1) —— oT Jacq., 
and (2) Jsomeris arborea, Nutt., in surfa 
surface view this conformation gives to the sheath a character- 
istic appearance. 
the genera investigated, the tracheal envelopes of Cleome 
and Polanisia are identical in the configuration and size of the 
constituent elements, while Jsomeris differs mainly in its larger 
tracheides. In some of the cells of the tracheal tissue of Jsomerts 
protoplasmic contents were still visible, but this might possibly 
have been a transient condition due to the immaturity of some 
of the seeds examined. 
The similarity of structure exhibited by the tracheal envelopes 
of these three genera is of special interest in view of their natural 
relationship and systematic position within the family. This 
raises the question of the possible value of this seed character, 
apart from its oe cecil as an accessory factor : 
in natural classificatio 
