TRANSPIRATION 19 



is an excellent plant to experiment with, as its woody twigs 

 are not greatly affected by cutting, and it absorbs water 

 almost as rapidly as it transpires. At the end of twenty- 

 four hours note the quantity of liquid that has disappeared 

 from each glass. This will represent approximately the 

 amount absorbed by the leaves from the twigs to replace 

 that lost by transpiration. Which twig has transpired 

 most ? Which least ? Note the condition of the leaves 

 on the different twigs ; have they all absorbed water as 

 rapidly as they have lost it ? How do you know this ? 

 Pluck the leaves from each twig, one by one, lay them on 

 a fiat surface that has been previously measured off by the 

 aid of a rule, into a square of about thirty centimeters 

 (twelve inches) to a side, containing nine hundred square 

 centimeters (one hundred forty-four square inches), and 

 thus form a rough estimate of the area covered by each 

 specimen. Measure the amount of water transpired by 

 filling up each bottle to the original level, from a common 

 medicine glass, or if this cannot be obtained, use a table 

 spoon, counting two spoonfuls to the ounce. Make the 

 best estimate you can of the number of leaves on each tree, 

 and calculate the number of kilograms (or pounds) of water 

 it would give off at that rate in a day. In one experiment 

 a peach twig containing thirty-one leaves gave off three- 

 quarters of an ounce of water in twenty -four hours ; how 

 many pounds would that be for the tree, estimating it to 

 bear eighteen thousand leaves ? As the tissues of a grow- 

 ing plant are much more active than those of a severed 

 branch, calculations of this kind are not likely to exceed 

 the truth, even when we take into consideration the fact 

 that the twig in the experiment has unlimited water, which 

 the roots of a growing plant have not always. 



These experiments may be varied at the option of the 

 teacher as time and opportunity may permit, so as to test 

 the absorbing and transpiring properties of any number of 

 plants or of the same plant at different stages of growth. 

 They will succeed best in dry, warm weather, as the work 

 of transpiration is then most active. 



