EFFECTS OF REGIONS OF VISIBLE SPECTRUM 785 



mission. Two filters were used, a yellow glass (Schott and Gen. OGl) 

 having a range of about 5100 to 31,500 A, and a red glass (Schott 

 and Gen. RG2) with a range between 5900 and 31,500 A. The trans- 

 mission in other parts of the spectrum was determined by difference, in a 

 comparison with transmission of the full spectrum of sunlight. 



The transmission values they obtained with whole leaves agreed 

 more or less with those of Seybold and others and need not be repeated 

 here. They found, in common with other investigators, that the light 

 that is transmitted by a leaf is entirely diffused when passing out of the 

 leaf, even when the incident beam is parallel; that long-wave radiation is 

 transmitted in greater percentage than short-wave radiation; and that 

 the short rays are diffused most and are most strongly absorbed by 

 chlorophyll. The red portions of a variegated Coleus leaf were found to 

 transmit higher percentages of the total incident radiation than were 

 green sections, but they transmitted less of the blue-green and yellow- 

 green components than did green sections. 



Schanderl and Kaempfert also found that the transmission values 

 of a leaf at different wave-lengths change as a result of movements 

 and orientation of the chloroplasts. By selecting leaves of Tradescantia 

 viridis, Pelargonium zonale, Adiantum cuneatum, and Coleus hyhridu^, 

 all of which were found to change the position of their chloroplasts under 

 different intensities of illumination, and by comparing the transmission 

 of these leaves in diffused hght or darkness with transmission in direct 

 sunlight, they found that 10 to 40 min. in direct sunlight was enough to 

 increase the transmission as much as 40 per cent. The short wave- 

 lengths were found to be influenced most. In the case of Tradescantia 

 viridis, the increase in transmission in the blue-violet end of the spectrum 

 was sometimes over 200 per cent. The products of photosynthesis in 

 the leaf were also found to affect the transmission. Accumulation of 

 starch in Tradescantia leaves caused a decrease in transmission of the 

 leaf. 



A number of previous workers determined the absorptive power of 

 chlorophyll in the leaf by comparing white parts of variegated leaves 

 with green parts. This method was used by Brown and Escombe 

 originally. Schanderl and Kaempfert have shown that this method is 

 not reliable because the white portions of many of these leaves are 

 filled with air, which greatly increases the reflecting powers of the cells 

 and results in lower transmission values. Since this condition does not 

 obtain in the green sections, it cannot be assumed that the colorless parts 

 of the green sections have the same absorptive power as the white sections 

 of the leaf. The extinction coefficient of chlorophyll can, therefore, not 

 be determined by difference. Seybold has also called attention to this. 

 Schanderl and Kaempfert attempted to determine the absorptive power 

 of chlorophyll by comparing the values obtained with green leaves with 



