PHOTOPERIODISM 489 



radiation in the blue and red portions of the spectrum was effective in 

 controlling flowering, whereas radiation in the green was ineffective. 



Funke (1936 through 1948) used radiation that had been passed 

 through appropriate filters to isolate various wave-length regions to 

 extend photoperiods of natural hght. The energy levels were unequal, 

 the red region probably having the highest value next to the unfiltered 

 radiation. Funke measured his results by date of flowering and on this 

 basis found four classes of plants, including examples of both long- and 

 short-day types. Some examples from each of the four classes follow: 



1. Red and unfiltered effective, blue ineffective, e.g., Anthemis tinc- 

 toria, Lycopus europaeus, Solidago virgaurea, Cosmos bipinnatus. 



2. Red, unfiltered, and blue effective, e.g., Mentha rotundifolia, Rud- 

 heckia speciosa, Perilla nankinensis (P. frutescens var. Crispa). 



3. Unfiltered effective, red and blue ineffective, e.g., Lepidium draba 

 (Cardaria draba). 



4. Unfiltered and blue effective, red ineffective, e.g., Iberis amara, 

 Siriapis alba {Brassica hirta). 



The responses in the first three classes can be explained by action 

 spectra of the type shown in Fig. 10-2, but this is not the case for the 

 fourth class. Funke (1948) observed that all species belonging to the 

 fourth class are Cruciferae. 



Wassink et al. (1950) examined the response of Brassica rapa, a species 

 of the fourth class, to supplementary irradiation in various wave-length 

 regions. Their findings fully support those of Funke in showing a strong 

 photoperiodic response to blue, violet, and infrared radiations, particu- 

 larly for floral development and stem elongation. Green, yellow, and 

 red radiations are essentially ineffective. In this work all plants were 

 given 10-hr photoperiods at a constant energy level of about 22 X 10^ 

 ergs/cm^/sec, with supplementary radiation of various colors for 8 hr at 

 an energy level of 1 X 10^ or 3 X 10'^ ergs/cm^/sec. 



Photostimulation of the pituitary and the accompanying testicular 

 growth of Peking ducks were studied by Benoit and Ott (1944). They 

 used equal incident energies in various wave-length bands isolated by 

 filters. Each duck was maintained in very dim blue light and was irradi- 

 ated every third day for 8 or 15 hr alternately for 10 periods. Response 

 was measured by the change in surface area of a testis exposed by lapa- 

 rotomy. They found the wave-length regions centering at about 6200 

 and 6800 A to be most effective, with effectiveness gradually decreasing 

 until 4400 A, where the response was the same as that of controls. Wave 

 lengths longer than 7000 A were ineffective. When the radiation was 

 reflected down quartz rods or tubes placed in the ocular cavity with the 

 ends resting on thin bones above the pituitary, red and blue were approxi- 

 mately equally effective in bringing about enlargement of the testes. In 

 these last experiments each duck was irradiated for 2 or 3 hr daily. 



