136 Our Field and Forest Trees 



made up the trunk and limbs is changed back by 

 fire into a vapor and a breath. 



The watery parts of the wood which pass off 

 as vapor when it burns have come into the body 

 of the tree by way of the root-hairs. Most of the 

 gases which go up and away in smoke and flame 

 have come in by the same lowly entrance — as 

 part of the earth-water. Before the gases and 

 the earthly treasures in this water could be made 

 over and built into the body of the living tree, the 

 water had to go into the leaves. Those are the 

 workshops where the soil water — or " crude 

 sap " — which the root-hairs take in from the 

 earth, is changed by foliage, air, and sunshine 

 working together, and made over into " elab- 

 orated sap." This elaborated sap is infant food 

 for pushing shoots and bursting buds, for length- 

 ening rootlets and for forming seeds. 



There is one regular line of travel inside the 

 tree for crude sap going toward the leaf labora- 

 tories, and another line of travel for the elab- 

 orated sap coming from them. 



The earth-water, or crude sap, mounts by way 

 of the youngest or " sap " wood. Nothing can be 

 prettier under the microscope than the cells or 

 vessels which the crude sap passes through on its 

 upward journey. The walls of some of them are 

 curiously pitted, and those of others are beauti- 

 fully marked with raised rings or corkscrew lines. 



Crosswise partitions separate each vessel from 



