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Rubject of more research than they are. It may be thought that the 

 clearness of the atmosphere in Colorado, bringing a superabundance of 

 sunshine, is a great gain to all life. It is so to many conditions of 

 human existence, but not to all, and under certain circumstances is di- 

 rectly injurious to vegetation. True it is that '' Light is the source 

 of life," but its very greatness and power require tempering, softening, 

 and restraining, like tire and water. Sunlight and warmth start the 

 machinery of a tree and produce the chemical combinations which are 

 necessary to its life. Under its influences the mineral substances, drawn 

 from the soil by its roots, are combined with the carbon and other mat: 

 ters received from the air through the leaves, and the resultants, 

 carbon and oxygen, are produced, the former for the building up of the 

 various parts of the tree and the latter by exhalation into the atmos- 

 phere, for the use of animal life. This machinery of the tree, under 

 proper conditions, works as steadily and smoothly as the best regulated 

 engine. But if the speed of an engine is increased too greatly there fol- 

 lows vibration, increased friction, a ialling out of adjustment, and soon 

 it becomes worn, broken, and useless. So with a tree, the rapid action 

 produced by the bright sun and clear air may draw too greatly upon 

 its means of subsistence, more or less limited in this dry region, and 

 the tree, unable to keep up the supply, dies. 



Thus we have found that trees in Colorado, especially in the section 

 around Denver and Colorado Springs, suffer principally from extreme 

 temperatures with sudden changes, and from lack of rain to supply the 

 needed moisture for the roots. When water is supplied artificially by 

 irrigation, they still suffer from insufficient humidity in the atmosphere 

 to provide moisture for the leaves and stems, from rapid evaporation 

 caused by the dryness and rarity of the atmosphere and the frequency 

 of winds, and from the clearness of the sky, or lack of cloud and mist to 

 intercept the dry, scorching rays of the sun, and to prevent the sudden 

 changes of heat and cold. Truly, indeed, this is not a favorable climate 

 for the growth of trees. But we have dwelt more particularly upon the 

 injurious qualities of the climate. The conditions are not all unfavor- 

 able, and notwithstanding the many drawbacks trees will and do grow 

 in Colorado and fulfill the objects for which they were created. 



ADVICE TO TREE-PLANTERS. 



We have already, from time to time, indicated some of the peculiar 

 modes of treatment necessary for the successful growth of trees in this 

 region, and a brief summary of these will be useful. 



Those localities should be selected for planting, if there be a choice, 

 which, by the configuration of the ground will be most protected. 

 Among the mountains, this will be on the northern slopes, where the 

 rays of the sun are least powerful and evaporation is least rapid. If pos- 

 sible the useful operation of plowing and cultivating the ground before 

 planting should be i^erformed. In this way the soil, besides being 



