SECRETARY'S REPORT 121 



plants. It is thus concluded that protochlorophyll and chlorophyll 

 as photoactivating pigments are probably not associated with photo- 

 morphogenesis and that some other pigment must be present which is 

 causing this reaction. 



Pigment analysis showed that the corn and bean plants treated with 

 radiation in the range from 730 to about 1,000 m/* developed from 50 

 to 100 percent more protochlorophyll, carotenoids, and, in the case of 

 bean, anthocyanin pigments per unit of fresh tissue than those kept 

 in the dark. On a per-plant basis, the increase varied from 200 to 

 300 percent depending upon temperature and intensity. 



Higher plants can grow "normally," the normal being considered 

 the growth form of a sunlight-grown plant, when a balanced spectrum 

 involving the proper proportions of blue and red radiation are pres- 

 ent. At moderate intensities of blue light, where there is sufficient 

 photosynthesis, growth is rather poor with most higher plants, and the 

 plants appear short and stunted. In red light of the same energy, 

 growth is rapid but the plants are tall and weak-stemmed. Since 

 the alga Chlorella pyrenoidosa is a standard test object that has been 

 studied in relation to photosynthesis and can be grown rapidly and 

 reproductively under precisely controlled conditions, it was consid- 

 ered desirable to test whether growth of Chlorella is dependent upon 

 the red-light reaction necessary for the growth of higher plants. 

 Chlorella cultures were grown under blue radiation from a mercury 

 lamp isolated at 435.8 mju, and the red cultures were grown in an 

 incandescent band from 635 to 670 m/i. Results thus far indicate that 

 Chlorella is not dependent upon the same photomorphogenic red-light 

 reactions as the higher plants, since growth in the blue-treated cul- 

 tures is similar to that in the red-treated cultures when equal quantum 

 energies are used. However, there is evidence that the blue cultures 

 contain more chlorophyll. Thus growth with Chlorella appears to be 

 dependent entirely upon the rate of supply of the products of photo- 

 synthesis. The other photochemical reactions do not appear to be 

 limiting as in higher plants. 



Gas-exchange studies made in a Warburg manometric apparatus 

 have indicated that in Chlorella there is no detectable increase in 

 respiration rate with radiation of wavelengths beyond 730 m/i and 

 there is, likewise, no photosynthesis. Thus these radiations that pro- 

 duce such marked growth reactions in higher plants produce no 

 measurable reactions in Chlorella. 



A second phase of the research has dealt with the effect of growth 

 regulators on salt uptake and water exchange by plants. The par- 

 ticular reference plant used was black valentine bean and the growth 

 regulator was ammonium 2,4-dichlorophenoxyacetate acid. The up- 

 take of salts was measured continuously by a recording electronic 



