72 



ESSENTIALS 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 

 Fig. 44. Diagram to illustrate Secondary at first extended 

 Growth in a Dicotyledonous Stem. ^^^^-^^ ^^^ toward 



R, the first-formed bark ; p mass of sieve-cells ; ^^ circumference 

 ifp, mass of sieve-cells between the original 



wedges of wood ; fc, cambium of wedges of of the Stem, beCOnieS 



wood; ic cambium between wedges; 6, groups compressed into 



01 bast-cells ; fh, wood of the original i\edges ; J^ 



ifh, wood formed between wedges ; x, earliest thin plates SO aS tO 



wood formed ; M, pith. ^^^^ medullary rays. 



These are, as already stated, of use in storing the food 

 which the plant in cold and temjierate 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 



