786 BIOLOGICAL EFFECTS OF RADIATION 



tliose obtained after the chlorophyll had been extracted from these 

 leaves, the same leaf being used for both determinations. This method 

 gave for the chlorophyll absorption 70 per cent in white light, 90 per cent 

 in violet-green, 63 per cent in green-yellow and 68 per cent in red and 

 infra-red. It is doubtful, however, whether this method is much more 

 accurate than the other. 



From extensive studies of isolated upper epidermises of leaves of all 

 kinds, Schanderl and Kaempfert (36) obtained maximum transmission 

 values of 98 per cent with epidermises of shade plants and minimum values 

 of 15 to 25 per cent with those of desert plants or plants growing in high 

 altitudes. The latter also caused the incident radiation to become much 

 more diffused than did the former. Colorless epidermises transmitted 

 about equally all wave-lengths, but those containing anthocyanin acted 

 as filters, reducing particularly the percentage of blue-violet radiation. 

 Hairs, resins, or waxes on an epidermis not only caused a pronounced 

 scattering of the incident radiation, thereby reducing markedly the total 

 transmission of the epidermis, but also absorbed more strongly the shorter 

 wave-lengths. The authors call attention to the fact that waxy coatings 

 are commonly found on fleshy fruits and succulent leaves and stems. 

 Since such structures have a high energy-absorbing capacity and hence 

 could be injured more readily by intense radiation than thinner struc- 

 tures, it is suggested that these coatings may serve more to reduce 

 the intensity of the incident energy than to check loss of water by 

 transpiration. 



By studying separately the transmissions of the palisade and spongy 

 mesophylls of leaves of Cyclamen persicum and Ficus elastica, the authors 

 found that if the radiation passing through the palisade and entering 

 the spongy mesophyll is placed at 100 per cent, that of the spongy meso- 

 phyll of Ficus elastica would be only 5 per cent and that of Cyclamen 

 persicum 40 per cent. The lower percentage transmission of the spongy 

 mesophyll is attributed, first, to the fact that it receives only highly 

 diffused radiation, and, second, that it is filled with air spaces that, in 

 many cases, cause total reflection. When the spongy mesophyll was 

 filled with water its transmission power increased. Under ordinary 

 conditions the palisade mesophyll absorbs much more radiation than 

 the spongy mesophyll because of its greater chlorophyll content. The 

 structure of the spongy mesophyll is such, however, as to enable it to 

 utilize much more efficiently the diffused radiation it receives. The 

 presence of hairs and other epidermal coverings on the lower surfaces 

 of leaves is also thought by the authors to cause a reflection back into the 

 leaf of the radiation which would pass out of the epidermis if it were 

 smooth. 



The structures of plants are so closely related to their light relations 

 that these authors suggested, instead of the ecological designations 



