566 SHAVINGS EXAMINED MICROSCOPICALLY. 
sections of wood, and in our plate are represented by the 
largest openings. In some of the succulent plants, however, 
they are to be seen in a more striking manner. It is only 
necessary to tear a stalk of rhubarb or celery apart to find 
that fine fibres appear which are the last things to be ruptured ; 
these are the spiral ducts, and constitute the "stringiness" 
of old specimens of vegetables. In our wood shavings we 
also observe other points of interest, more especially if the 
sections be cut across the "grain" or direction of the main 
growth. First let us examine the upper of our figures (Pl. 
10, fig. 1), whieh represents such a slice cut from a stick of 
oak. This has been taken from a common kind of wood 
and well representing the grand group of plauts to which it 
belongs, that is to say the Hxogens, or outside growers. 
Our lower figure, on the other hand, represents a section of. 
a stem of sugar-cane, showing.the mode of growth of an 
Endogen, or inside grower. And these two names at once » 
designate the point upon which we wish to dwell; the mode 
of growth of woody stems as shown by means of the micro- 
scope. These figures have been carefully drawn from pho- 
tographs taken for the purpose, and are, therefore correct 
representations of the objects. Looking now at our cross- 
grain shaving of oak, we notice first, per somewhat 
unevenly all over it, large openings, which are the spiral 
ducts; in some parts they. appear to be more closely congre- 
gated together, forming, as it were, rows which are contin- 
uous after the manner of rings, increasing in dimensions 
from the centre of the stick towards the circumfereace- 
These show us how the wood grows. -At first, when it is but 
a sapling, there is very little woody tissue present, as is 
bend from its fragility, and the moss of it is made ap 
of simple cellular tissue. This constitutes the pith of the 
stem, and varies in dimensions in different plants; in the 
s elder being very large, in the oak of small size. Through 
.. the large spiral ducts the sap freighted with matter for the 
= Tie up of new tissues, is carried upwards to the leaves; 


