428 RADIATION BIOLOGY 



the endosperm caused greening of the embryo, but contact with the 

 cotyledons was most effective. The greater the surface of contact, the 

 more intensive the greening. Embryos laid on the endosperm greened 

 more on the side of contact than on the other side; and the greater the 

 length of time the embryo and endosperm were left in contact after 

 germination, the greater was the intensiveness of the greening. Embryos 

 removed from their own endosperms and placed on other endosperms of 

 their own species or a different species still formed chlorophyll in the 

 dark. From these results, Schmidt concluded that a chlorophyll agent 

 ("Chlorophyll-Agens") is transferred from endosperm to embryo which 

 transforms the chlorophyllogen of the embryo to chlorophyll. But 

 attempts to get greening with disintegrated endosperms were fruitless. 



Bogorad (1950a) investigated the greening of P. jeffreyi seedlings in 

 the dark and found that extirpated embryos from ungerminated seeds 

 did not form chlorophyll in the dark either on synthetic media or on 

 various extracts of endosperms; that illumination of the germinated 

 embryo caused greening; and that, within limits, seedlings synthesized 

 chlorophyll more rapidly and in greater amount, the longer they had 

 been in contact with the megagametophyte after germination. Embryos 

 excised from the endosperm at different stages of greening continued to 

 form chlorophyll The rate of chlorophyll formation in the germinating 

 embryo after extirpation increased up to the eighth day of contact with 

 the megagametophyte and then decreased. Embryos that have been 

 greened by illumination lose part of their chlorophyll during storage in 



the dark. 



Bogorad's results demonstrated that the amount of chlorophyll formed 

 in darkness by the unextirpated embryo was equal to the amount of 

 chlorophyll formed in the extirpated embryo by illumination {ibid., p. 

 227). From this quantitative correspondence of the amount of chloro- 

 phyll produced, it appears that the chlorophyll precursor is present in 

 the embryo and is converted to chlorophyll either by a substance trans- 

 ferred from the endosperm or by action of light. 



In an attempt to determine the nature of the chlorophyll agent, 

 Bogorad followed the transfer of material from the megagametophyte 

 to the sporophyte. He observed the transfer of organic matter, iron, 

 and both inorganic and organic compounds of magnesium, but he could 

 obtain no evidence as to its nature. Although magnesium compounds 

 were transferred, the magnesium in the chlorophyll of the sporophyte 

 never exceeded the magnesium initially present in it. It is unhkely that 

 a holoenzyme is transferred from endosperm to embryo. 



The chlorophyll in conifer seedlings grown in the dark has the same 

 absorption bands as that formed in plants in the Hght (Schmidt, 1924). 

 Smith and Koski (1947-1948) found the ratios of chlorophyll a to chloro- 

 phyll b to be 3 to 1 for Pinus coulteri and 3.7 to 1 for P. jeffreyi. For 



