TREES 123 



and have a good hold upon the paper on each side of 

 the stems, when pasted down. Do not use the strips too 

 long nor too plentifully. The flowers and leaves should 

 be fastened so that they cannot move, but too many strips 

 do not look well. After a plant is nicely fastened, cover 

 ; t with the left hand part of the paper and press under 

 several large books until dry. Then write its name and 

 description in the place on the right hand page where 

 there is the most room. 



48. *Trees. 



The value of trees to man is very great. We have 

 learned that trees take in carbon dioxide and give out 

 oxygen. This is of more importance in our cities than 

 in the open country for there are many fires in houses 

 and factories, all of which are producing vast quantities 

 of carbon dioxide. Although the wind blows part of 

 this away and the rain washes some of it into the ground, 

 yet it is most important that we have as many trees as 

 possible in our cities. Trees, as well as all other plants, 

 give off a huge amount of water by transpiration and 

 change the climate of a locality very much. See Sec- 

 tion 40. Trees also reduce the violence of winds. Final- 

 ly, trees are beautiful. 



While trees, are of very great value in cities they are 

 of still greater value to the nation in whose forests they 

 grow. When rain falls upon bare ground most of it runs 

 off, wearing the soil away and doing no good. After the 

 rain is over there is very little water left in the soil, and 

 this soon dries up in the bright sunlight. If the ground 

 is dry there will be no streams or rivers soon after the 



* See Appendix. 



