44 . SEVENTH REPORT. 



THE VITALITY OF SEEDS. 



W. J. BEAL. 



(Professor of Botany, Agrieiiltiiral College.) 



This paper will be published in full in the Proceedings of the American Society for the Promotion 

 of Agriculture for 1905, an& also in the Botanical Gazette. 



"COLOR" STIMULUS AND VITAL FUNCTIONS OF PLANTS. 



J. B. DANDENO. 



Sunlight aifects the vital functions of both plants and animals. What 

 people are in the habit of calling sunlight is, however, composed of 

 several separable and distant elements. These individual portions 

 (colors) of the solar spectrum also exert specific influences over the 

 vital activities of plants or parts of plants, in a fairly constant and 

 definite manner. It has been so customary to use the term light as 

 though it were a single inseparable stimulus, that most physiological 

 experiments have been made with regard to light as a unit. Hence, 

 we have the term heliotropism, photosynthesis, and the like, conveying 

 the idea that light acts as a single stimulus, instead of the resultant 

 of a number of separable stimuli. 



As has already been pointed out (Science, Nov. 6, 1903, p. 604), 

 no very decisive investigations have been made to determine the effects 

 of the individual portions of the spectrum. Moreover, the statements 

 concerning what has been done, seem to be somewhat contradictory 

 and indefinite. Pfeffer (Ewart's trans, p. 104) states: '*The relative 

 activity of the diftereut rays of the spectrum has not been precisely 

 determined, and hence it is impossible to say whether the curves for 

 the retarding, j)hototonic, and formative action exactly coincide or not. 

 In general, however, it may be said that these curves, like that showing 

 lieliotropic effect, attain a maximum in the more refrangible rays, fall 

 nearly or quite to zero in the green or yellow part of the spectrum, and 

 frequently, though not always, again" rise to a second smaller maximum 

 in the red end of the spectrum." Pfeffer states further (p. 101) : "On 

 the other hand it is the less refrangible rays which are most active in 

 photosynthesis, and to a less degree in the development of chlorophyll." 

 But Belzung states (Anat. & Physiol. Veg., p. 77) : '"Le verdissement 

 acquiert toujours son maxinnim d'intensit^ dans la lumiere jaune." 

 In Belzung's figure showing curve for development of chlorophyll, the 

 colors appear in the following order : yellow, green, blue, red. violet. 

 This is different from the latter part of Pfeffer's statement given above, 

 because he places red as the part having greatest eff'ect. Even in 

 Pfetfer's own work, as quoted by Sachs (Text-book of Botany, p. 745, 

 740), there seem to be two different results relating to what Sachs 

 called assimilation ( photosynthesis) . He arranges them in one place, 

 in the following order: yelloAV, red, green, blue; and also (p. 740); 

 yellow, orange, green, red, blue, violet. Pfeffer (Physiol, of Plants) 

 seems to have abandoned the figures already given by him, and quoted 



