320 PLANT GROWTH SUBSTANCES 



darkness. When C. eiigametos is treated in this manner and the filtrate 

 exposed to red, yellow, or green light for several hours there is no loss of 

 the capacity to induce sexuality in darkness. The effect of blue or 

 violet light is different. A filtrate from a male culture exposed to blue 

 or violet light retains, for less than 30 minutes, the ability to induce 

 sexuality in male cells in darkness. When the exposure lasts for more than 

 30 minutes the filtrate loses the capacity to activate either male or 

 female cells. Filtrates from female cultures are unable to induce sexuality 

 in female cells after exposure to blue or violet light for more than 30 

 minutes, but exposure of female filtrates to blue or violet light for 75-90 

 minutes causes a change into substances capable of making male cells 

 function sexually. Filtrates illuminated for more than 90 minutes are 

 unable to induce sexuality in either sex. 



Although red light is incapable of causing a formation of sexual 

 substances in C. eiigametos it is capable of causing a formation of a 

 precursor (P) of them. When Moewus (9) made either male or female 

 cells motile in darkness by means of glucose and then illuminated with 



o 



red light (5890 A) there was an excretion of the precursor into the water. 

 When a filtrate from such a culture was exposed to blue light for 20-30 

 minutes it contained a substance (9S) capable of making female cells 

 sexually functional. This disappeared after illumination for 30 minutes, 

 but when illumination was continued for 30-40 minutes (a total illumina- 

 tion of 60-70 minutes) the filtrate contained the male sexual substance 

 (cf S). The male substance disappeared after illumination for 10 minutes 

 and neither it nor the female reappeared with further illumination. 

 Illumination for approximately 100 minutes resulted in the formation 

 of an end substance (E). When written as a formula the series of changes 

 may be expressed as follows: 



P -^ 9S -^ cTS -^ E 



In the change from precursor to end substance there is a gradual 

 decrease in percentage of precursor in the filtrate and a corresponding 

 increase in the percentage of end substance. When the change has 

 progressed to a certain stage the ratio between the two results in the 

 female sexual substance, and a further progressive change in the ratio 

 results in the male substance. Moewus (9) demonstrated this by testing 

 the cllect of various combinations of precursor and end substance in 

 inducing sexuality of male and female cells in darkness. For C. eiigametos 



