Th'F.E Sli:.\lS S7 



slice ot cilliL-r while or \clli)W w ,ilcr-lil\" slciii on a 

 ]jiecc of i^lass and, holding; it up to the li;^lu, a fine 

 sort of lacc-work will he seen. rhcsc arc the culls 

 which con\c\' air and water throiiL;h the stem up 

 to the lea\e^ and llowers. Or if we examine a 

 flower petal w ith a ma,L;nif\-in,L; i^lass we shall find 

 it to he entirel)' composed of minute cells. 



In these little spaces are stored \er\- man\- 



srKM IIK YKLLOW STKM OK WHITK 



WATKl'i-I.II.Y. WATKk-l.n.V. 



and very different materials, all necessar\- to the 

 L^rowth of a tree ; we shall tr\- and learn ahout 

 them by dei^rces ; at i)resenl we must endeaxour 

 t(; obtain a clear idea (»f their structure. 



A tree-stem increases in size \-earl}- h\- the 

 i^rowth of fresh cells within the outer hark, and 

 this actixe increase of tissue is due mainlv to what 

 is called the cambium layer, which is developed 

 only in the sprini^ and siuiimer and does not exist 



