246 BOTANICAL GAZETTE [September 



In his very extensive work Klebs has always maintained that the action of 

 red light was due to the fact that it has high photosynthetic action. Schanz's 

 work suggests that the effect may be due in part to the fact that it eliminates 

 detrimental ultra violet rays. 



This very important work of SCHANZ merits checking up and extending. 

 The work with ultra violet light has been largely with artificial spectra much 

 richer in ultra violet than the solar spectrum, and too little exact study has 

 been made of the formative effects of the ultra violet of the latter spectrum. 



A very noteworthy piece of work by Garner and Allard, 8 reviewed in 

 detail elsew 7 here in this journal, should be mentioned in this connection. It 

 is possible that the remarkable effects they obtain from length of day is due 



* 



to the fact that it modifies the nitrogen carbohydrate ratio of which Fischer, 

 Kraus and Kraybill, 9 and others have made so much as a determiner 

 of the course of development, whether vegetation shall dominate or there 

 shall be a balance of vegetation and reproduction. 



In the small dosages of light used in phototropic and photo-growth response, 

 the most effective region of the spectrum on the basis of equal energy value lies 

 at A. 505 fxfx for the sporangiophore of Phycomyces; at A. 467 fxfx for the coleoptile 

 of Avena; and at X 494 /a/a for Volvox, as previously given. Perhaps with the 

 high dosage of natural illumination the effective region shifts still more to the 

 right as is indicated by Schanz's work. 



A comprehensive study of the formative effect of light on plants is much 

 needed to see to what degree its formative action is due to synthetic activity, 

 to the so-called photo-growth responses, to various effects of ultra violet rays, 

 and to other effects not included in these. — Wm. Crocker. 



Effect of light exposure on plant growth. — Garner and Allard 10 have 

 grown plants under different conditions of light exposure, and have made a 

 special study of the tendency to become reproductive or to remain vegetative 

 under varying daily lengths and intensities of exposure. Several varieties of 

 tobacco and soy bean were mainly used in the experimental work, although 

 numerous other species of annuals and biennials were used to check the results 

 attained. 



Plants were grown in pots, buckets, or boxes, and at the desired time 

 each day were moved into dark chambers which were placed in the field. For 

 the last season's work, large dark houses were constructed, in such a way that 

 plants could be moved in or out at any time. Time of exposure to light 



8 Garner, \Y. \\\, and Allard, H.A., Effect of relative length of day and night 

 and other factors of the environment on growth and reproduction in plants. Jour. 

 Agric. Res. 18:553-606. 1920. 



Q Bot. Gaz. 67:445-446. 1919. 



10 Garner, W.W., and Allard, H. A., Effect of relative length of day and night 

 and other factors of the environment on growth and reproduction in plants. Jour. 

 Agric. Res. 18:553-606. 1920. 



