o 



2 Mississippi Valley Horticultural Society. 



peach tree can form, collect and keep separate such a number of distinct and 

 discordant secretions ? 



In all exogenous trees the inner and older portion is much harder and 

 dryer than the exterior. This change is due to the consolidation of the inte- 

 rior wood, by the deposition in its tissues of woody matter. The portion of 

 the stem in which this has taken place thus acquires great toughness and du- 

 rability, but it is no longer fit to perform any office in the living system save 

 that of mechanically supporting the rest, since no sap can pass in any way 

 through the now lillcd-up channels. This heart wood always displays a de- 

 posit of coloring matter not observable in the younger or outside layers. 

 Thus in the wood of the apple or pear, the handsome orange color of the 

 heart wood marks the period of rest, and as far as assisting growth is con- 

 cerned, it is (d rest forevermore. It is through the newer layers or sap-wood, 

 therefore, that the larger portion of the sap ascends, and these in their turn 

 become inclosed by others, and are at last consolidated like the more aged 

 ones into heart-wood. 



The sap-wood is enclosed by the bark, which, like it, is formed in regular 

 layers ; though these are much thinner, and can not be so plainly distin- 

 guished. The layers of bark are formed from the interior, so that the oldest 

 ones are on the outside. These are gradually lost, either by decay or by fall- 

 ing olT; so that it is seldom that the same number of rings can be traced in 

 the bark as in the wood, although an additional one is formed each year. As 

 the new layer of wood is formed on the outside of the previous one, at the 

 point at which it was in contact with the bark, and as the new layer of bark 

 is added to the inside of the previous one, at the point at which it was in 

 contact \\ith the wood, it is obvious that they are produced at the same spot, 

 and that the newest layers of both will always be in contact with each other. 



Between these, always at the close of the season's growth, will be found a 

 glutinous fluid composed of gum and sugar. The gumminess of this fluid is 

 at once perceived by its mucilaginous i)roperties, and that it contains sugar 

 is known by the sweetness of its taste. This is the elaborated sap, ripened 

 and prepared, after the wood growth has been perfected, for being converted 

 into an organized tissue the succeeding year. This substance, called the 

 cambium layer, can he readily seen by stripping the bark from almost any 

 twig, in the early part of spring. Later in the season this layer is gradually 

 organized into cells, and from these are formed the ducts and cellular por- 

 tion of the season's woody layer. If a wound be made in the bark, and 

 through to tlie sai)-wood, a similar glutinous substance is thrown out from 

 the cut edges, and by the conversion of this into woody tissue, the wound is 

 gradually healed. li^ven if a complete ring be cut away from the wood and 

 around the body of the tree, this substance will exude from the edges above 

 and below, till the si)ace fills up and the two edges reunite. This then is the 

 material which the tree has matured and stored uji within itself during au- 

 tumn, lit ))i(!ot the (exigences of the coming spring. The swelling buds and 

 expanding leaves excite the rootlets, these begin to absorb the food within 



