MICHIGAN ACADEMY OF SCIENCE. 63 



leaves in comparison with the size of its stem, has condiu'tiiio; vessels of enor- 

 mous size, enabling the plant to supply through its small and long stem the 

 needs of the leaves. Many roots are similarly developed. The elm root, 

 well known to the youthful would-be-smoker, has vessels similar to those of 

 the grape stem. These vessels, as are also those of other stems, are modi- 

 fied cells, which by losing their intervening end partitions, have been thrown 

 into one long canal which has been termed a vessel, and hence the name vascu- 

 lar plants as applied to all such as have vessels. 



The amount of water lil)erated by a plant may be realized by giving 

 some figures. A birch tree having about 200,000 leaves gives out about 

 400 liters (125 gallons approximately) in 24 hours. A sunflower of good 

 size about one gallon in three days, and an acre of cabbage about 550,000 

 gallons in four months. But certain plants, as has already been pointed out, 

 differ widely from others in amount of water liberated, e. g., a beech tree 

 gives out about ten times as much as a spruce, the weight of the leaf being 

 used as a basis for calculation. 



To realize more fully the o]5eration which this loss of water involves, let 

 us give one special instance: The amount of air required to carry off the 

 water given out by transpiration is enormous. At a temperature of 82 F., 

 an oak requires about one million cubic feet of air per day, a sunflower 1500 

 cubic feet per day, and an acre of cabbage about 25 million per day of 24 

 hours. These figures are calculated from the amount actually transpired, 

 and from the amount of water vapor in suspension in aii' at a given tempera- 

 ture. 



Agricultural College, Mich. 



