REPORT OF THE SECRETARY 115 



was somewhat too low for good growth. Plowever, Dr. Meier found 

 the growth of algae to be better under these lamps than in daylight. 

 The algae were illuminated for 12 hours daily at intensities of 150 

 to 300 foot-candles. The temperature during the illumination 

 periods was 24° C, and during the dark periods, 22° C. 



INFLUENCE OF LIGHT IN EARLY GROWTH OF OAT SEEDLINGS 



The oat seed on germination develops roots and a shoot. The 

 latter consists of the first internode and of a sheathing structure, the 

 coleoptile, in which the young leaves are enclosed. Elongation of 

 the internode proceeds rapidly in darkness but is inhibited by light. 

 This organ has the function of raising the coleoptile with the em- 

 bryonic shoot through the soil and into the air where it may develop 

 normally. Thus in deeply planted seeds the internode receives little 

 or no light and therefore elongates until it approaches the soil surface 

 when its growth ceases. 



Earlier studies by Dr. Johnston on the relation of light to internode 

 development are being continued by Dr. Weintraub along the follow- 

 ing lines: 



1. Relation between amount and rate of growth of first internode 

 and intensity of continuous illumination in various portions of the 

 visible spectrum. Preliminary results indicate that intensity of red 

 light (6500 A.) necessary to produce a distinct inhibition is exceed- 

 ingly low — of the order of 0.0000001 erg/mm."/sec., whereas the 

 sensitivity appears to be considerably less at other wave lengths thus 

 far studied. 



2. Influence of short periods of illumination on development of 

 internodes in seedlings grown subsequently in darkness. The great 

 sensitivity to light is shown by preliminary experiments in which 

 marked or complete inhibition of growth is caused by a minute or 

 less of low intensity (1 foot-candle) illumination. 



3. Influence of alternating light and dark periods. The precise 

 effect of light has been found to depend upon the age (developmental 

 stage) of the seedling and upon its previous history. Changes 

 from dark to light, or the reverse, are accompanied by marked after- 

 effects of the preceding treatment. 



4. Interrelationships between growth of first internode, coleoptile, 

 and first leaf as influenced by light and by temperature. Evidence 

 of such relationships has been obtained, and further studies are being 

 made in an attempt to determine the cause and effect in them. 



5. Mechanism of the response. Attempts to explain the observed 

 behavior in terms of growth-hormone content of the plants await 

 the development of suitable methods for the determination of the 

 hormones. Study of such methods is in progress. 



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