258 



PHYSIOLOGY OF GROWTH AND CONFIGURATION 



As Molisch 1 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 temperature, especially if the branches to be forced 

 are immersed for from ten to twelve hours in water at 30 to 35°C. or above. 

 Fig. 105 shows a hazel branch the right side of which was subjected to Molisch'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 Surroundings. — Higher plants usually grow only 

 when they may absorb oxygen; when the oxygen sup- 

 ply is cut off growth is immediately stopped. Noba- 

 kikh 2 has shown, however, that when certain con- 

 ditions are fulfilled seed-plants may be made to grow 

 in an atmosphere free from oxygen. He placed the 

 plants in a solution of glucose. A double object was 

 thus attained: the plants were furnished with nutri- 

 ent 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 214), the amount of oxygen ab- 

 sorbed by germinating seedlings 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 (see page 241 ) . 



resting "udThf wa^i^atTrl The amount of oxygen contained in the surround- 

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



rate of 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. 3 



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 als Mittel zum Treiben der Pflanzen. Jena, 1909. 



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

 St. Petersburg, 1904. Nabokich, A. J., [Idem], Temporare Anaerobiose hohere Pflanzen. Landw. Jahrb. 

 38: 51-194 1909- 



3 Jaccard, Paul, Influence de la pression des gaz sur le developpement des vegetaux. Rev. gen. bot. 

 5: 289-302, 348-354. 382-388. 1893- 



