12 ELEMENTS OF BOTANY 
outside of the wood in early spring is a fact well known 
to the schoolboy who pounds the cylinder cut from an 
alder, willow, or hickory branch until the bark will slip 
off and so enable him to make a whistle. The sweet 
taste of this pulpy layer, as found in the white pine, the 
slippery elm, and 
the basswood, is a 
familiar evidence of 
the nourishment 
which the cambium 
layer contains. 
With the increase 
of the fibro-vascular 
bundles of the wood 
the space between 
them, which ap- 
pears relatively 
large in Fig. 40, be- 
comes less and less, 
and the pith, which 
Fre. 44. Diagram to illustrate Secondary at first extended 
Growth in a Dicotyledonous Stem. 
freely out toward 
f, the tirst-formed bark; p, mass of sieve-cells; the-erreun ference 
ifp, mass of sieve-cells between the original . ; 
wedges of wood; fc, cambium of wedges of of the stem, becomes 
wood; é¢e, cambium between wedges; b, groups 
of bast-eells; fh, wood of the original wedges ; 
ifh, wood formed between wedges; *, earliest thin plates so as to 
wood formed; JM pith. 
compressed into 
form medullary rays. 
These are, as already stated, of use in storing the food 
which the plant in cold and temperate climates lays up 
in the summer and fall for use in the following spring, 
and in the very young stem they serve as an important 
channel for the transference of fluids across the stem from 
