228 



PHYSIOLOGY OF GROWTH AND CONFIGURATION 



As Molischi has shown, even though the resting period may not be ter- 

 minated by subjecting the plant to medium temperatures, it can be brought to a 

 close by application of high temperaturey.especially if the branches to be forced 

 are immersed for from ten to twelve hours in water at 30° to 3S°C. or above. 

 Fig. IDS shows a hazel branch the right side of which was subjected to MoUsch's 

 warm-bath treatment, while the left side was untreated. Nine days' after the 

 treatment the right side was already in full bloom, while the buds on the left 

 side were still in the resting condition. 



§2. Dependence of Growth and Configuration upon the Oxygen Content of 

 the Air. — Higher plants usually grow only when they 

 may absorb oxygen; when the oxygen supply is cut 

 off growth is immediately stopped. Nabokikh^ has 

 shown, however, that when certain conditions are 

 fulfilled seed -plants may be made to grow in an 

 atmosphere free from oxygen. He placed the plants 

 ^ "^ >^ HI in a solution of glucose. A double object was thus 

 TW "^ 1 B^ attained: the plants were furnished with nutrient 

 ^4 ^J»Sli material and, at the same time, the products of 

 fermentation harmful to growth were allowed to 

 pass into the solution. These results were later sub- 

 stantiated by other authors. As has been pointed 

 out above (page 194), the amount of oxygen ab- 

 sorbed by germinating seedHiigs increases, as the 

 growth rate becomes more rapid. The march of the 

 respiration rate in germinating seeds may be expressed 

 by a grand curve of respiration which agrees, in 

 general, with the grand curve of growth (seepage2i8). 

 JSg bu'dVfn^'ltl'S The amount of oxygen contained in the surround- 

 the right side of the branch ing atmosphere exerts a marked influence upon the 

 was so treated. ^^^^ ^^ growth. An excess of this gas, as well as a 



deficiency, decreases the growth rate and may even cause growth to cease 

 entirely. On the other hand, if the pressure of the air does not vary too far 

 from the normal, in either direction, then such a change produces an accelera- 

 tion of growth. This brings out the very noteworthy fact that growth under 

 normal atmospheric pressure is less rapid than when the pressure is somewhat 

 higher or somewhat lower than normal.' 



It appears that oxygen is one of the most important factors in the life of 

 microorganisms. For some organisms oxygen is essential, others can exist a 

 long time without it, and still others can reproduce only under conditions where 

 it is entirely absent (see Part I, Chapter VIII). Microorganisms may thus be 

 separated into aerobes and anaerobes, according to their oxygen requirement. 



1 Molisch, H., Das. Warmbad a!s Mittel zum Treiben der Pflanzen. Jena, 1909. 



' Nabokikh, A. I., Temporary anaerobiosis of higher plants. [Russian.] Dissert. New Russia Univ. 

 St. Petersburg, 1904. Nabokich, A. J. [Idem], Temporftre AnaSrobiose hohere Pflanzen. Landw. Jahrb. 

 38: 5I-I94. 1909. 



' Jaccaid, Paul, Influence de la pression des gaz sur le d^veloppement des v6g6taux. Rev. gin. bot 

 5:289-302,348-354.382-388. 1893. 



