CH. IV] BLOOM. Ill 



india-rubber tube. The vessels and intercellular spaces at 

 the upper (free) end of the stick are to be secured by an 

 india-rubber tube wired on and closed by being folded 

 down parallel to the branch and again wired. The 

 U tube is placed in a jar of water so that the stick is 

 immersed, and mercury is poured into the long arm : 

 after a varying time air is seen to issue in fine streams 

 from the lenticels, — that is if they are open. Fifteen or 

 20 cm. of mercury give sufficient pressure. 



(126) Bloom. 



The character of the leaf-surface has an effect on 

 transpiration, as may be shown in the following way^ 

 Bring into the laboratory a pot of Kleinia or Cotyledon^ 

 or some other succulent plant with a good bloom. It 

 is best to bring the pot into the laboratory because 

 if the leaves are cut before they are wanted they are 

 likely to get rubbed. Cut off two similar leaves (or two 

 similar twigs) and pierce each specimen with a piece of thin 

 copper wire to serve as a hook by which to hang it up. 

 Paint the cut surfaces with lard : weigh the specimens, 

 hang them in a dry room for 12 or 24 hours, and weigh 

 them again. This will give the normal transpiration of 

 the two specimens. Now remove the bloom from one 

 specimen by delicate sponging with water at about 35'' C. 

 When it is dry weigh both again, and once more expose 

 them to the dry air of the laboratory for 12 or 24 hours. 

 The cleaned specimen should now transpire relatively 

 more than the other. 



1 See Garreau, Ann. Sc. Nat. S. 3, T. xiii., p. 339. 



