ORR—TRACHEAL TISSUE IN CAPPARIDACEAE. 255 
Maerua, Forsk., and Niebuhria, DC. 
Between these two genera there is practically no distinction 
in the structure of the envelope. There are two superimposed 
layers of tracheides, deeper than those of the preceding species, 
and possessing bands of thickening somewhat similar to those 
found in Capparis spinosa, but not so clearly visible in surface 
view. 
I 2 
Fic. 4.—A portion of the tracheal envelope of {1) Apophyllum anomalum, 
F. Muell., and (2) Maerua parvifolia, Pax, in surface view. 
Crataeva, Linn., and Euadenia, Oliv. 
These two genera are closely related, and in the characters 
of the tracheal tissue surrounding the embryo there is no dis- 
tinction between them. In surface view the tracheal elements 
appear much larger in area than those described for other genera, 
but they are extremely shallow, and the irregular configuration 
of the lateral walls, which is such a distinctive feature in many 
types, is entirely absent. There is practically no indication of 
thickening on the walls when the sheath is examined in surface 
view, and it is only by means of pressure applied to the cover- 
glass, and careful focussing, that the fine annular bands are 
brought into view. 
The presence of a well-defined layer of cells with thickened 
walls of a cellulose nature, underlying the tracheal tissue, is a 
characteristic feature of the enveloping sheath of these genera. 
This layer is evidently a store of reserve-cellulose destined for 
the use of the embryo. 
It will be evident from the descriptions and figures of the 
tracheal envelopes found in the genera included under Cappareae 
that there is a considerable variation in the extent and arrange- 
ment of the thickening on the walls of the tracheides. This is 
