CONTROLLED ENVIRONMENTAL CONDITIONS 331 



Shirley's findings stated earlier in this chapter that maximum chlorophyll 

 development occurs in plants in light intensities that are near the minimum 

 of light intensity that insures survival of the green plant. 



Limiting of nitrate supply leads to an increase in chlorophyll and caroti- 

 noids when plants are grown in the greenhouse during the winter; but the 

 reverse is true with higher light intensities. Also under higher intensities 

 the bro^\^l pigment increases. Limiting potash and phosphorus increases 

 the chlorophyll on the wet weight basis but has little effect on the dry 

 weight basis. Growth of plants in soil gives higher chlorophyll and caroti- 

 noids than growth in nutrient solutions. Limiting nitrates, potash, and 

 phosphorus has little effect on a/h or c/x ratios. 



Environmental Conditions Modify the Microchemistry and 



Anatomy of Plants 



A study -^ was made of the effect on the microscopic, chemical, and 

 anatomical changes brought about in plants by the several growth condi- 

 tions mentioned early in this chapter. In one set of experiments the plants 

 were gro\\Ti in the artificial-light room under 5, 7, 12, 17, 19, and 24-hour 

 day lengths. The conditions in the room were: temperature, 25° C (77° F) ; 

 light intensity, 780 foot-candles at the beginning falling to 352 foot-candles 

 at close; relative humidity, 80 per cent; CO 2 concentration, about 0.3 per 

 cent. Plants were also grown in an ordinary greenhouse without extra 

 light and CO2, in a gantry crane house with 6 hours of artificial illumination 

 at night, and in a gantry crane house with 6 hours of artificial illumination 

 at night and about 0.3 per cent CO2. The artificial illumination of the gan- 

 try crane started mth 383 foot-candles and decreased during the experi- 

 ment to 141 foot-candles. The experiments were run during March, April, 

 and early May. 



In short daily illumination the plants were low in carbohydrates and 

 protein reserves and showed less differentiation of tissue. In the longer 

 daily illumination the plants showed greater carbohydrate reserves without 

 a corresponding increase in differentiation of tissues and protein reserves. 

 Nitrates were abundant in the tomato plants in all the houses except the 

 control and two gantry crane houses. Nitrates were low in buckwheat in 

 the 17, 19, and 24-hour day lengths as well as in all the greenhouses, being 

 lowest in the gantry crane CO2 house. 



In artificial light the maximum height and differentiation of tissue 

 occurred in 12-hour day for tomato and the 17-hour day for buckwheat. 

 The tomato plant was injured by artificial light in the 17-hour or longer 

 day. Continuous illumination produced thinner leaves with palisade cells 

 shorter or lacking. In the gantry crane houses the thickness of the leaves 

 was variable, and the thinner leaves showed an increase in the number of 

 stomates except in continuous light. 



The size of the fibrous root system was proportional to the top gro\vth 

 of the plant. The storage root of the four-o'clock showed maximum develop- 



