THE CANADIAN HORTICULTURIST. 



Fig. 2218. 



Fig. 22ig. 



Fig. 2220. 



Fig. 2221. 



Fig. 2218. — The healing of a torn wound, also cut too long. 



Fig. 2219. — A well-healed wound, the result of a properly made cut. 



Fig. 2220. — Result of leaving a stub. 



Fig. 2221. — Result of removing scions from grafted limb before the cut has been entirely healed over. 



a tree, or a large-sized branch or root be cut 

 through, it would show the bark, the light 

 colored sap-wood and the darker central 

 portion, or heart wood. Just between the 

 bark and the sap-wood, if we could see it, is 

 a layer of very delicate tissue known as the 

 cambium. 



Cambium. — The cambium is the only tissue 

 that retains the power of active growth. It 

 can best be seen by removing the bark on 

 some actively growing tree, and so sensitive 

 is it that exposure to air will kill it in a few 

 minutes. It appears as a soft slimy or 

 doughy substan-e that can be scraped off 

 with the thumb-nail. The cambium is a 

 very delicate substance, easily affected by 

 frost or wet, and may be easily crushed or 

 torn. It is the giving away of the cambium 

 that causes the bark to strip off from the 

 wood. During the growing season, the 

 cambium gives rise to a layer of wood on 

 the inside and a layer of bark on the outside, 

 and a thick layer of cambium is left between 

 the new wood and bark to carry on the 

 growth of the tree next year. 



The Bark. — In bark, nature has formed 

 a perfect covering for the delicate cambium 

 beneath. Being corky on its outer surface, 

 the bark of a waterproof covering to keep 



in the sap and at the same time exclude ex- 

 ternal moisture from decaying the cambium. 

 Bark being somewhat soft and spongy in 

 its construction, contains considerable air, 

 which, acting as a non-conductor of heat, 

 serves the purpose as a dead air space in a 

 building, and keeps the cambium from being 

 frozen or dried out. From this it appears 

 how careful nature is of the delicate parts 

 of the tree, and in all our operations of prun- 

 ing we should exercise similar care. The 

 orchard should always receive the best 

 thought and practice of its owner, and 

 should never be left to the tender mercies of 

 the hired man or the itinerant pruner. 



The Wood. — The light-colored portion of 

 the stem is the sap-wood. It is through 

 this that the sap containing its dissolved 

 mineral elements, finds its way to the leaves. 

 In the leaf the watery portion of the sap is 

 evaporated, and the remainder, under the 

 action of light, is combined with the carbon- 

 dioxide of the air, and returns downward 

 through the cambium to be used up in 

 growth. The darker portion of the stem is 

 the heart-wood, which is dead tissue, whose 

 only use is to give support to the tree. 



The Root. — The root presents the same 

 appearance when cut across as the stem, 



