72 PLANT PHYSIOLOGY. 



ale, 251. It is best to make up a stock for use of the class, but it should 

 be made freshly each year. 



A more direct proof that a mineral salt maybe absorbed in solution 

 through roots would probably be found by growing seedlings in a dilute 

 solution of lithium citrate, and subsequently testing with the spectroscope 

 the bands given by holding sections of the tissue in the bunsen flame. 

 But perhaps such absorption is too obvious to need special experiment. 



i 



A. Absorption (/;) of Gases. 



28. What is the structure of a typical absorbing system for 

 gases ? 



Answer by a study of a typical leaf. 



Construct a diagram of a leaf as a gas-absorbing apparatus, 

 bringing out the path of the gas from the outside world to the 

 cells where it is to be used. 



For a " typical " leaf, one of those of a mesophytic deciduous tree or 

 shrub, such as Syringa or Maple, would be best. Much easier to obtain 

 in winter and to section and examine is Ficus elastica, which while not 

 " typical " is sufficiently so from the present point of view. Owing both 

 to the firmness and the high degree of differentiation of its tissues, this 

 leaf is an excellent one for studies on leaf anatomy, particularly for 

 beginners. 



Observation of the anatomy of leaf or stem shows a system 

 of air-spaces communicating with the air outside through 

 stomata. To be efficient, all air-spaces should thus communi- 

 cate with stomata, or their equivalent lenticels. 



29. Are the intercellular spaces through long distances in the 

 plant continuous with stomata? 



Answer by Experiment 14. 



EXPERIMENT 14. This may be tested by forcing air into one part 

 of a plant and noting whether it will issue from stomata at a dis- 

 tance. Select a leaf with its full petiole of a Rubber-plant (Ficus 

 elastica) ; slip a small stout rubber tube, a foot long, over the end of 

 the petiole and tie it firmly ; to the other end of the tube fasten a 

 bicycle-pump ; place the leaf-blade under water (to render visible any 

 air issuing from the leaf), pump air vigorously into the petiole, and 

 observe result. 



Leaves of Calla (Richardia) are very good for this, and the floating 

 leaves of water-lilies, etc., are especially effective ; but most leaves 

 readily give the result. 



