16 
ORGANOGRAPHY. 
BOOK I. 
are those of a spiral vessel. That the partitions really exist, 
as has been correctly stated by Dutrochet, there can be 
no doubt, notwithstanding the denial of the fact by Link and 
others. They may be seen with the naked eye in the vasiform 
tissue of the Cane, the Bamboo, and many other plants. 
Vasiform tissue is therefore to be considered composed of 
cylindrical cells, the sides of which are covered with oblong 
granules, looking like dots, and arranged with their principal 
axis across the tube, and the united ends of which cause the 
partitions discoverable upon a longitudinal section. It is these 
partitions, moreover, that produce the external appearance of 
transverse transparent lines. 
Slack takes, however, a somewhat different view of the 
nature of the dots. He considers them to be transparent 
spaces in the sides of the cells, and caused by the separation, 
at intervals, of a spiral fibre whose convolutions are partially 
and firmly united in the spaces between the dots ; and he re- 
presents a case of vasiform tissue from Hippuris in illustration 
of his position. This is a very ingenious explanation, and 
perhaps the ti ue one, of what is a most puzzling circumstance, 
if the dots are really granules, viz. the great regularity with 
which ihey are arranged. But it requires further confirm- 
ation. 
The vasiform is the largest of all kinds of tissue. The holes 
which are so evident to the naked eye, in a transverse section 
of the oak or the vine, are its mouths; and the large openings 
in the ends of the woody bundles of Monocotyledonous stems, 
as in the Cane, are also almost always caused by the section 
of vasiform tissue. The stems of Arundo Donax, or of any 
larger grass, is an excellent subject for seeking it in; it can be 
readily extracted from them when boiled. 
In the centre of some of the bladders of the cellular tissue of 
many plants there is a roundish nucleus, apparently consisting 
of granular matter, the nature of which is unknown. It was 
originally remarked by Francis Bauer, in the bladders of 
the stigma of Phaius Tankervilliae. A few other vegetable 
anatomists subsequently noticed its existence ; and Brown, 
in his Memoir on the mode of impregnation in Orchideae and 
