250 ORR—TRACHEAL TISSUE IN CAPPARIDACEAE. 
ways, giving to the tissue a distinctive appearance when viewed 
under the microscope. This thickening is in the form of annular 
and spiral bands or reticulations, which in some cases are found 
on the surface walls of the cells, and in others are confined to 
the lateral walls. 
Such elements as those referred to above possess the form and 
structure of tracheides, indicating that the specialised layer 
surrounding the embryo is tracheal in character. 
Such tracheal tissues are not entirely unknown in the seeds 
of living plants, for Beauregard * refers to a similar layer in his 
description of the seed of Daphne, and their presence in the seeds 
of certain other Thymelaeaceae was subsequently recorded by 
Guérin.| This latter author compared this pellicle with its 
tracheides to the tracheal sheath of the Cycadofilicales, but 
regarded it as representing in the Thymelaeaceae the vestige 
of a primitive structure 
In the Capparidaceae, such a tissue, with its different types of 
structure, suggesting separate lines of development within the 
family, would appear to be not merely vestigial, but actively 
functioning at some period in the growth of the seed. 
Before the seed is liberated, the tracheal envelope is in close 
association with the vascular strand of the funicle, and may 
possibly function for a time at least as an accessory water-supply 
system forthe embryo. On the other hand, its late development 
seems rather to imply that it plays a more important part in the 
economy of the seed at the time of germination. It is found 
that the apex of the tracheal sheath projects slightly into the. 
micropylar pore, and, in the presence of moisture, its absorptive 
properties, already referred to, would ensure a supply of water 
being conveyed to all parts of the embryo, and especially to the 
radicle through the infolding of the envelope in that region. 
It would appear, then, that in the seeds of the Capparidaceae 
the enveloping sheath acts as a sponge, absorbing moisture 
through the micropyle, and constituting a kind of “ water- 
jacket ’’ surrounding the embryo 
-- The investigation of the sheath characters of the different 
genera was carried out mainly on seeds taken from herbarium 
specimens, no other source of supply being available at the time, 
and there are of necessity numerous gapsin thesequence. A full 
list of the seeds examined will be found at the end of this paper, - 
and when possible the actual specimen from which they were 
obtained has been indicated. The nomenclature followed is that 
contained in Bentham and Hooker’s Genera Plantarum. 
* M. Beauregard in Bull. Soc. Bot. Fr., xxiv (1877), p. 385 
t P. Guérin in C. R. Ac. Sc. Paris, clvi (1913), p. Kes atidin ‘Aidt, ee Bot. 
Buitenzorg, ser. 2, xiv (1915), p. 1. 
