HO OUTLINES OF PLANT LIFE. 



Floating plants have opportunity to obtain it both from the 

 water and from the atmosphere. Land plants, although their 

 roots are surrounded by a comparatively concentrated solution 

 of carbon dioxid, do not take up appreciable quantities by 

 these organs. On the contrary, the absorption of this gas 

 seems to depend entirely upon those cells which contain 

 chlorophyll. The stomata, which allow the internal spaces 

 free communication with the outside air, are important organs 

 for facilitating the absorption of this gas. Its continued ab- 

 sorption depends upon its continuous removal from the cell 

 sap in the manufacture of food. 



EXERCISE XXX. 



To show the permeability of stomata for air and their communication 

 with the system of intercellular spaces. 



Fasten a leaf with a long petiole air-tight in a rubber cork, through 

 which also passes a short glass tube. Fit the cork into a bottle holding 

 sufficient water to cover end of petiole. Attach a filter-pump or air- 

 pump to glass tube. Observe whether air bubbles leave the end of the 

 leaf stalk. 



Reverse the leaf, so that the blade is immersed, and make same ob- 

 servation. Where do bubbles appear ? Is there any difference between 

 upper and lower sides ? 



190. Photosynthesis. — The process by which carbohydrate 

 foods (sugar, starch, etc.) are produced is called photosyn- 

 thesis * The steps in the process are not thoroughly known ; 

 indeed they can only be guessed at, and the theories need 

 not even be stated here. The final product is not neces- 

 sarily the same in all plants, but in many it is cane 

 sugar. Starch appears later in the form of minute granules 

 in the interior of the chloroplasts. It is probably formed 

 as a means of removing some sugar from the cell-sap 



* This term seems to be more generally approved than photosyntax, 

 which was first proposed as a name for this process. 



