SAP ACTION. 



FRED. A. WATT. 



IN order to understand this subject 

 we must first ascertain the condi- 

 tions under which sap is first pro- 

 duced, what it is, and how it circu- 

 lates. 



To do this we must first know some- 

 thing of the structure of those parts of 

 the tree which serve as channels, or 

 ducts, and those other parts which 

 gather the sap and dispose of the waste 

 after it has completed its mission. 



To begin with, the tree is composed 

 of small structures, too small for the 

 naked eye to distinguish. Each struc- 

 ture is, at least for a time, a whole in 

 itself, containing solid, semi-solid, and 

 fluid parts which differ in their chemical 

 nature. These structures are the cells, 

 and when a large number of them are 

 united in close contact they form a cel- 

 lular tissue through which the sap 

 passes from the roots to the leaves, and 

 from the leaves to the growing parts 

 of the young tree, or shoot. 



This cellular tissue is superseded by 

 another tissue which is much stronger 

 and which takes up the work of the 

 cellular tissue, when the tree becomes 

 too large to be supported by the weaker 

 form. It is more solidly formed and is 

 composed of elongated cells which are 

 joined together in a series with their 

 ends overlapping. This is known as 

 woody fiber. The cellular tissue now 

 exists in the tree stem only in the pith, 

 and in the medullary rays which we 

 may see in the grain of any hard wood, 

 radiating from the pith. 



With the statement, then, that these 

 tissues form the timber, and that the 

 bark and roots only present a modifica- 

 tion of the same structures, we will 

 pass to the tree as we see it with the 

 naked eye. 



If we saw the trunk of a tree, of any 

 considerable size, squarely in two, we 

 find three forms which differ in solidity, 

 rigidity, and appearance; namely, the 

 heart-wood, sap-wood, and bark. The 

 heart-wood is the firm, solid wood sur- 

 rounding the center of the tree, the 

 sap-wood is the softer wood outside 



the heart-wood, while the bark forms 

 the skin or outer covering for the 

 whole. 



Trees grow from the center outward, 

 hence the present sap-wood will in 

 time become heart-wood and be cov- 

 ered by a new layer of sap-wood, and 

 the present heart-wood is simply sap- 

 wood which has become solidified by 

 the deposit within its tissues of resin- 

 ous and other matter secreted by the 

 tree. It is now useless for sap- carrying 

 purposes and seems to exercise only 

 the function of supporting the tree in 

 its position. It is through the outer, 

 younger layer or sap-wood that the 

 sap ascends. 



Now, if we examine the end of our 

 stick more closely we see a series of 

 rings, clearly marked, circling from 

 the center of the tree and ranging in 

 size from the tiny one which encloses 

 the pith, to the large one which forms 

 the outer surface next to the bark. 

 They are caused by a constant annual 

 deposit and outward growth, by which 

 a layer is added to the outer surface of 

 the sap-wood each season. Hence, by 

 counting these we may determine the 

 age of the tree. Less distinct rings 

 may appear but they will not deceive 

 us as we know that they are caused b)- 

 a cessation of growth, which may have 

 been caused by drouth. 



As a general rule these rings are 

 more distinct in trees inhabiting a 

 climate where vegetation is entirely 

 suspended by the cold after each layer 

 is formed. In warmer regions they are 

 not so distinct. This is especially in- 

 teresting when we study the fossils of 

 trees which in many cases show a 

 great difference in climatic conditions 

 in the early ages from those we have 

 at the present time. 



The layers of bark are much thinner 

 than those of the wood and are not so 

 readily distinguished. They are formed 

 from the interior so that the oldest are 

 on the outside. The older ones fall 

 off, however, so that we cannot trace 

 as many rings in the bark as we can in 



