_ 94 - NUTRITION OF PLANTS 



WITHOUT CHLOROPHYLL. 



50. Symbiotes. Root-tubercles of berseem. 



(a) Roots seen with the naked eye showing the tubercles. 

 (6) Section of a tubercle fixed and stained with iodine examined under the 1/12 

 inch oil-immersion objective to see the nitrogen- fixing bacteria and the store of starch. 



RESPIRATION. 



51. Necessity of oxygen for growth. Pollen-tubes grown in a sugar solution 

 beneath a cover-slip. Only those pollen-grains grow which are within reach of the oxygen 

 diffusing in from the edges of the cover-slip. 



