PHYSIOLOGY OF NUTRITION. 



dish G' contains mercury, over which we pour a thin layer of 

 water, or we may use water alone instead of the mercury. The 

 glass dish G" contains strong potash solution, and in it is a slab 

 of glass on which stands the flower pot with its plants. The 

 bell-glass Ggl is placed over the seedlings with its rim dipping 

 into the mercury or water. The tubulure of the bell-glass is fitted 

 with a cork, through which passes a bent glass tube connected up 

 with the U-shaped tube Z7, containing pieces of pumice stone 

 soaked with potash solution, together with small pieces of caustic 

 potash. If we expose the apparatus to the light for about two 

 days (preferably to direct sunlight, at least periodically), the 

 cotyledons become starch-free. If we now place the pot and 

 plants in the window again, apart from the apparatus, considerable 

 quantities of starch quickly collect afresh in the green cells of the 

 cotyledons. 1 



If we wish to cultivate plants for a long time in an atmosphere 

 free from Carbon dioxide, it is well to proceed as follows, so as to 

 prevent too great and injurious accumulation of moisture in the 

 air under the bell-glass. We use a very large bell-glass. This is 

 dipped into mercury covered with a layer of olive oil, or we may 

 employ a bell-glass with a well-ground rim, and place this on a 

 rough ground glass plate, the junction being made air-tight by 

 smearing with a mixture prepared by melting together 3 to 4 parts 

 of lard, and 1 part of wax. This mixture may be preserved in a 

 closed vessel, protected from dust, and may often be employed, 

 even, e.g., in experiments with the air-pump. The apparatus is 

 put together as represented in Fig. 18. Vessels containing 

 Calcium chloride may also be introduced in order to reduce still 

 further the moisture of the air. 



The fact determimed by Moll 2 is very interesting, viz., that in 



many cases a piece 

 of leaf produces no 

 starch in air free 

 from Carbon di- 

 oxide, although it is 

 still in organic con- 

 nection with another 

 portion of the same 



FIG. 19. Apparatus for experimenting on assimilation. leaf which beino 1 in 

 (After Moll.) . r , 



air well supplied 

 with Carbon dioxide is vigorously assimilating. We experiment 



