92 
HISTOLOGY OF VEGETABLES. 
at an angle of 45° to the length of the fibre, and the 
pores lying on one surface have the direction of the central 
spot at right-angles to that on the other surface; the 
outer or bordering lines correspond ; hut if the thin part 
of a fibre be examined, it often happens that both the 
upper and under surface are in focus at the same time, 
and then the appearance of a cell with a crucial nucleus, 
as shown by c in Fig. 80, will be presented. This 
fact is even more strikingly exemplified in Salisburia 
adiantifolia , the pores being of much larger size. Por- 
tions of two of the woody fibres of this plant are repre- 
sented by a b in Fig. 80 . At a the central pore on 
one surface of the fibre is shown, and at B the two 
opposite sides of the same fibre, in which the crucial 
appearance is most strikingly exemplified. At a, in 
Fig. 77 , a section through two contiguous woody 
fibres of the same plant is represented, by which it will 
be seen how these peculiar pores are formed. 
