TRANSPIRATION. 213 



(6) Set two cut twigs of Lime in water ; expose one (^4) to direct 

 sunlight, the other (B) to weak diffuse light. After an hour, 

 apply the cobalt test to a few leaves of each, and note the marked 

 difference in the rate of reddening of the paper in contact with the 

 lower surface in the two cases. 



(c) Weigh cut twigs of Willow and of Lime, as nearly as possible 

 similar in weight, also in size and number of leaves. Lay the two 

 twigs together on a dry table or shelf. Weigh them at intervals 

 during two days ; note that the Willow transpires much more 

 actively than the Lime, and that its leaves become quite withered 

 and dry at a time when the Lime leaves are still fairly fresh. 

 Test a wilting leaf of each plant with cobalt papers the stomata 

 are closed in Lime, but open even in the withering leaf of Willow. 



(d) Take a pot plant of Aspidistra or Ficus, cover the pot and 

 soil with sheet rubber, and put the plant in bright light for half an 

 hour ; weigh it, then set it back in direct light for two hours, and 

 weigh again note the loss by transpiration. Now set the plant in 

 weak diffuse light for half an hour, weigh it, put it back in the 

 diffuse light for two hours, and weigh again note the greatly 

 reduced loss by transpiration in weak as compared with strong 

 light. Repeat the experiment in the reverse way putting the 

 plant first in weak and then in strong light. 



(e) Set a Tropaeolum plant or a Bean seedling in a dark place, or 

 under a cover, overnight ; in the morning pick off a leaf and test 

 with cobalt paper, noting the time required for reddening, then set 

 the plant in the light, and in half an hour test another leaf in the 

 same way or pick off a leaf at intervals of five minutes and test 

 them with the cobalt paper, to ascertain whether the stomata are 

 open. Remove the plant to darkness again, and at intervals test 

 the leaves with cobalt paper, to ascertain whether the stomata 

 have closed. 



(/) Cut off a Tropaeolum or other thin leaf and let it lie on the 

 table until somewhat withered ; then cut off a fresh leaf from the 

 plant, and test the two leaves together with a cobalt paper. The 

 stomata in this plant close on wilting. Let the two leaves be ex- 

 posed to bright light ; the wilted leaf does not wither any further 

 even after some hours, while the fresh leaf dries up rapidly because 

 it does not close its stomata. 



(g) Get fresh shoots of Alisma or Menyanthes, and let a cut leaf 

 of one of these plants remain on the table, along with a cut leaf of 

 Tropaeolum, until the leaves are withered and half-dried. Then 

 apply the cobalt paper test, and note that there is still vigorous 

 transpiration from the wilted leaf of the marsh plant, in which 

 the stomata remain open, while in Tropaeolum this is not the case 

 owing to the rapid closure of the stomata on wilting. 



(h) That salt-solution causes the stomata to close may be shown, 

 without using the microscope, by means of cobalt paper. Water 



