306 PHYSIOLOGY OF GROWTH AND CONFIGURATION 



a temperature of 4-o°C. Alpine forms of ordinary plants that grow also at lower 

 altitudes are markedly different from the lowland forms, and this is partly due to the 

 different temperature conditions of the two environments. The date of flowering is 

 generally much later for plants grown in a cold region than it is for other individuals of 

 the same form grown in a warm region, and this difference is related to differences 

 between the two regions with respect to the temperatures of the preceding autumn 

 and winter, as well as of the spring. Molisch introduced the warm-bath method for 

 breaking the dormant period and forcing the early formation of flowers, in shrubs, 

 etc. Shoots bearing dormant winter buds are submerged in warm water for half a 

 day, after which treatment the buds immediately proceed to develop flowers under 

 greenhouse conditions, while untreated shoots do not respond to the same conditions 

 until the season is much farther advanced. 



2. Influence of the Oxygen Content of the Surroundings on Growth and Confi- 

 guration. — It appears that ordinary plants may be influenced, as to their rates of 

 growth, by alterations in the oxygen content of the surrounding air. For microorgan- 

 isms the oxygen supply is of the utmost importance. Aerobes (such as acetic acid 

 bacteria) require oxygen for their development, while anaerobes can develop without 

 it. Obligate anaerobes (such as butyric acid bacteria) are poisoned by oxygen, but 

 facultative anaerobes (such as yeasts) thrive either with or without a supply of this 

 element. Some aerobes require less oxygen than others. The mould Mucor develops 

 the usual hyphal weft and sporangiophores when growing on the surface of a suitable 

 medium, with plentiful air supply, but its growth is similar to that of yeasts when it 

 grows at the bottom of a mass of liquid medium; this difference in configuration may be 

 due to the difference in oxygen supply. 



3. Influence of Other Gases on Growth and Configuration. — The carbon dioxide 

 supply influences the growth of ordinary plants; it may be either too low or too high for 

 healthy development. Some seedlings are very sensitive to small traces of ethylene 

 and of other toxic gases in the air about them, and plants are generally injured by 

 considerable amounts of illuminating gas in the soil surrounding their roots. If the 

 supply is very low, some poisonous gases accelerate the growth of ordinary plants. 

 Johannsen introduced the ether treatment for breaking the dormant period and 

 forcing the early formation of flowers, in shrubs, etc. Shoots bearing dormant 

 winter buds are enclosed for a number of hours in a chamber containing ether vapor, 

 after which treatment the buds immediately proceed to develop leaves and flowers 

 under greenhouse conditions, while untreated shoots do not respond to the same condi- 

 tions until the season is much farther advanced. 



4. Influence of Moisture on Growth and Configuration. — The rate of water supply 

 to plant or organ must generally be somewhat greater than the rate of water loss, 

 since growth is usually accompanied by the accumulation of water in the enlarging 

 tissues. As already pointed out, the water supply for ordinary plants is from the soil, 

 while transpiration represents the main form of water loss. Consequently, the mois- 

 ture condition of a plant may be altered (1) by a change in the power of the soil to 

 supply water to the roots, (2) by a change in the power of the roots to absorb water 

 that is in contact with their external surfaces, (3) by a change in the power of the air 

 (including the sunlight effect) to remove water vapor from the foliage, etc., (4) by a 

 change in the ability of the aerially exposed surfaces to hinder the evaporation of water 

 {i. e., to retard transpiration), or (5) by any two or more of these changes operating at 

 the same time. If the environmental conditions are such that the mean value of the 

 ratio of intake to outgo is less than unity, then the plant is unable to develop under 



