too 



BOTANY OF THE LIVING PLANT 



Uiulci- til'- ncirmul day-conditions of a temperate climate the light 

 and Icuiperrilurc [;dl within the hmits of mtensity necessary for Photo- 

 Syntliesis to proceed, wliile the Transpiration-Stream suppHes thesalts 

 required, inckiding those of Potassium and Iron. These necessary 



conditions being met, ;:/;« constnic- 

 lii'e process consists in the absorp- 

 tion of carbon dioxide, fixation of 

 the carbon, release of free oxygen, 

 and the appearance m the active cells 

 of material formed from the carbon 

 which has been fixed. Commonly, 

 though not always, it is starch 

 that makes its appearance, and it 

 is located in the chlorophyll cor- 

 puscles themselves. Starch may 

 iJien he recognised as the first 

 'oisible product of Photo-Synthesis 

 (Fig. 72). 



Naturally the demonstration of 

 such a gaseous interchange as 

 that involved in Photo-Synthesis 

 cannot be given so readily in 

 sub-aerial as in submerged plants, 

 and the latter are usually used for 

 this purpose. If a single shoot 

 of the common Canadian Water 

 Weed [Elodea) be fixed below the 

 level of water in a glass jar, with 

 the cut end of the stern pointing 

 upwards, and the whole be ex- 

 posed to the light, bubbles of gas 

 will be seen to be extruded in 

 succession from the cut surface, 

 and to rise through the water 

 (Fig. 7i)- These are bubbles of oxygen. Arrangements can easily 

 be made to collect the gas in bulk from a mass of specimens, and 

 to subject it to the ijsual tests. These bidibles of o.xygen are a visible 

 bye-product of Photo-Synthesis, and they may be used as a measure of 

 the activilv of the process. The bubbles are approximately of equal 

 size and the number of them liberated in a given time may be 

 couiitcd. In tliis way it may be shown that the activity is greater in 



A . Cliloropliyll gr.iriules in cells oi the leal of 

 Funaii\i, showing small starch-grains included in 

 thciii. 11 shows stages of division of the chloro 

 ph\-il granules. / shows the included starch- 

 uraiiis a.fter Ihe grainile h;is swollen in water. 

 (A'fle)-S.iel,,,) 



