114 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



INTLUENCE OF LIGHT IN EARLY GROWTH OF GRASS SEEDLINGS 



Further study of the spectral effectiveness of radiation for the 

 growth inhibition of the oats mesocotyl has indicated that the maxi- 

 mum response occurs at 6600 A. It is highly suggestive that both 

 chlorophyll a and a pigment as yet unidentified which has been found 

 in dark-grown oats seedlings exhibit an absorption band at this 

 position. 



A comparative study has been undertaken of some other species 

 of grasses that have been reported in the literature as having meso- 

 cotyls insensitive to light. All of those so far investigated have 

 been found to be suppressed by light although the intensities required 

 are much greater than in the case of Avena. 



Since the growth of the oats mesocotyl is decreased, even in dark- 

 ness, by higher temperatures it is of interest to compare the effects 

 of temperature and of radiation. The high temperature inhibition 

 appears to differ fundamentally from the light inhibition inasmuch as 

 the growth of other organs of the seedling, notably the roots, is also 

 greatly suppressed in the former case. Some preliminary experi- 

 ments have indicated that in certain varieties of rice, on the other 

 hand, mesocotyl growth is greater at higher temperatures. 



INFLUENCE OF CULTURAL CONDITIONS ON THE GROWTH OF ALGAE 



The influence of culture conditions on the photosynthetic behavior 

 of the alga Chlorella fyrenoidosa has been subjected to further 

 investigation. The growth cycle of this organism has been studied in 

 relation to light intensity, carbon dioxide concentration, and the 

 composition of the nutrient solution. This work is far from com- 

 plete but has suggested certain changes in the composition of the 

 nutrient solution and in the design of the apparatus. Equipment 

 is being constructed for the continuous culture of algae in order 

 to obtain completely reproducible quantities of biological material 

 for irradiation experiments. 



Experiments were also conducted to ascertain suitable light condi- 

 tions and culture media for optimum growth of the alga Haema- 

 tococcus pluviaUs in preparation for research on the comparative 

 effects of short wave lengths of the ultraviolet on the green pigment, 

 chlorophyll, and the red pigment, haematochrome, in algae. 



As a result of inquiries regarding the use of algae in industry 

 and because of its importance to producers of kelp, Irish moss, agar, 

 and alginic acid in the defense program, a paper is being prepared 

 containing the latest statistics and information about the economic 

 uses of algae. 



