The Occurrence of a Tracheal Tissue enveloping 
the Embryo in certain Capparidaceae. 
Sy 
MATTHEW YOUNG ORR, 
Assistant in Laboratory, Royal Botanic Garden, Edinburgh. 
With four figures in the text. 
THE ovules and seeds of the Capparidaceae have certain 
peculiarities of structure which, so far as is known, are not 
possessed by those families to which it approximates in systematic 
position, and one of the most striking is the presence in the seed, 
in some of the genera at least, of a highly specialised cellular 
tissue surrounding the embryo. 
In ripe seeds this tissue is to be found adpressed to the inner 
wall of the testa, to the internal configuration of which it closely 
conforms, but from which it can be easily detached by careful 
dissection. On its inner side it is in close contact with the 
embryo, which it completely envelops. 
In longitudinal sections of the seed this envelope or sheath 
has the appearance of an additional internal seed-coat,* and in 
some cases its intimate relationship to the included embryo is 
further emphasised by an infolding of the tissue between the 
radicle and the cotyledons. 
When perfectly dry the whole envelope has an opaque, 
silvery appearance and can be easily distinguished from the dark- 
coloured testa, but when moistened it visibly expands and be- 
comes transparent. Microscopic examination of this pellicle 
shows that it is composed of one or more layers of cells, which 
are differentiated in a remarkable way. The extent of this 
modification and the particular form it has taken. vary in 
different genera, but its main features are more or less constant 
for each genus. The various types of envelopes will be described 
individually, but the distinctive features of this tissue and its 
possible function may be briefly referred to at this point. 
In the seeds of the species examined, the layer, or layers, 
referred to above are composed of cells without protoplasmic 
contents, the walls of which elements are strengthened in various 
_ * This third seed-coat is referred to by Baillon (Nat. Hist. of Plants, vol. iii, 
1874, p. 152, note 1). 
[Notes, R.B.G., Edin., No. LX, January 1921.] 
