CHAP. I. 
WOODY TISSUE. 
19 
smaller. It must, however, be observed, that the fibres of 
this plant, as used in linen-making, are by no means in a 
state of final separation, each of the finest that meets the 
naked eye being in reality a bundle of tubes. While some do 
not exceed 3 oVo of an inch in diameter, others have a diameter 
as considerable as that of ordinary cellular tissue itself; in 
Coniferae the tubes are often 2 io or ^ioi and in the Lime they 
average about -j^q. Link states {Elementa^ p. 85.) that they 
are very large in trees of hot countries, as, for instance, the 
Brazilian coffee. 
There are three distinct kinds of woody tissue : — 
1. That in which the walls are not occupied with either 
granules or glands sticking to them, or in which the former 
are of very rare occurrence. (Plate II. fig. 1.) This is the 
finest and the commonest of all ; and is also the most genuine 
state of woody tissue. 
2. That in which the walls have uniformly considerable 
numbers of granules of regular size sticking to them in a 
scattered manner. (Plate 11. fig. 3, 4, 5.) These granules 
have been and are still considered by many anatomists as 
pores in the sides of the tissue. They have been, in parti- 
cular, so described and represented lately by Adolphe Bron- 
gniart in Cycadeae, in which the tubes are large, and the 
appearance very conspicuous. (Annales des Sciences^ vol. xvi. 
tab. 21.) But I think it possible to demonstrate that this is 
an optical deception, and that the supposed perforations are 
semitransparent granules. In the first place, no colourless 
light passes through the supposed pores in any case ; on the 
contrary, they are dark, and have a solid appearance at all 
times, except when, at a certain distance out of the focus of 
the microscope, they become luminous. Secondly, if they 
were holes, they would, at least, be seen open when the tissue 
is dry and contracted, although they might close up when it 
becomes swollen with moisture. That, however, they never are : 
on the contrary, they are more opaque when dry than when wet. 
Thirdly, they become more and more opaque as the magnify- 
ing power with which they are viewed is increased; a circum- 
stance which seems incompatible with perforations. Finally, 
and it is this which will possibly be regarded most conclusive, 
c 2 
