96 



and indirectly as well, by affecting the other climatic condi- 

 tions. The habit of growth of the plants is thus altered and 

 probably the amount of photosynthesis per unit leaf area. 

 Such effects, if they are general for plants grown under glass, 

 would obviously be of importance in their bearing on plant 

 physiological experiments conducted in^reenhouses. It would 

 seem that growth behind even a single thickness of ordinary 

 glass is quite different from growth in the open, and that in 

 applying conclusions drawn from greenhouse experiments to 

 plants grown under outdoor conditions this fact woiild have 



to b e taken into account. 



"'he Forest Station . 



The nine series of four-week cultures grown in the open 

 and the three series grown under glass include all the soy- 

 beans of the experiment except one series which was grown in 

 the woods near the Laboratory of Plant Physiology at Baltimore. 

 This series, the Baltimore Forest Station, was located, as has 

 been noted, about 150 yards from the exposed and covered cul- 

 tures at Baltimore. The behavior of the plants grown in the 

 woods seems to support very clearly the assumption upon vrhich 

 the behavior of the exposed and covered cultures is explained. 

 Only the evaporation was measured for this station but the suji- 

 shine intensity was, of course, very low due to the shading 

 and screening effect of the leaves of the trees above the ex- 

 perimental plants. The temperature would also probably be 

 considerably lower than the temperature experienced by the 

 exposed and covered plants. The modification of growth habit 

 in the case of tfie forest plants is very striking as can be 

 seen by an inspection of the r)lant graph for the Baltimore 



