SEED GERMINATION 533 



4. PHOTOBLASTISM AS A FUNCTION OF INNER CONDITIONS 



4-1. INFLUENCE OF COATS ENVELOPING EMBRYOS 



Most of the positively or negatively photoblastic seeds germinate well 

 in darkness or light when the fruit or seed coats are removed (Becker, 

 1913; Magnus, 1920; Gardner, 1921; Hesse, 1924; Bihlmeier, 1927; 

 Bohmer, 1928; Axentieff, 1929; Hutchings, 1932;Resuhr, 1939a; Evenari, 

 unpublished work). 



Fruit or seed coats are not always the decisive parts, since it was shown 

 for lettuce that only after the removal or puncture of the endosperm was 

 the photorequirement of the seed abolished (Evenari, unpublished work). 

 Very often the whole coat does not need to be removed in order to obtain 

 this effect. It suffices to puncture the seed coat (Lehmann, 1912), to 

 abrase it (Gardner, 1921), or to rub it between the fingers (Resiihr, 

 1939a). 



But there are cases of both positively and negatively photoblastic seeds, 

 where the removal of the coats does not affect the photoblastism of the 

 seeds (Axentieff, 1929) or affects it but little (Bohmer, 1928). For the 

 negatively photoblastic seeds of Phacelia it has been shown that it is 

 enough to remove the chalaza end of the seed coat to bring about germi- 

 nation in light. The removal of other parts of the seed coat does not 

 affect germination (Magnus, 1920; Bohmer, 1928). Other experiments 

 have shown that the same chalaza end of the seed is the seat of its 

 photosensitivity {ibid.; Resiihr, 1939a) and that thermodormancy occurs 

 only with intact chalaza ends (Bohmer, 1928). Something similar was 

 observed for the positively photoblastic Nicotiana, where the removal of 

 the "Keimdeckel" (i.e., that part of the seed coat which is penetrated 

 by the radicle) stimulates germination in darkness (Bihlmeier, 1927). 

 For many gramineous fruits it has been proved that the hulls that 

 envelop the caryopses are responsible for the photoblastism of the grains, 

 since dehulled grains germinate in light and darkness ahke (e.g., Gassner, 

 1910, 1911a,b; Maier, 1933a,b). 



When the dehulled grains of Chloris, which are indifi"erent to light, 

 are wrapped in filter paper, their photoblastism is restored, and they 

 again need light for their germination (Gassner, 191 la, b). The same 

 was observed for decoated lettuce seed (Evenari, unpublished observa- 

 tions). When Phacelia seeds that had been made light-indifferent by 

 removal of the seed coat at the chalaza end were covered with filter 

 paper at this part, they were again inhibited by light in their germination 

 (Bohmer, 1928). 



Seeds made nonsensitive to white light by decoating are no longei' 

 affected by inhibiting blue light (Resiihr, 1939a; Leggatt, 1948), and 

 thermodormancy does not occur (Borthwick and Robbins, 1928; Evenari, 

 unpubfished observations for lettuce). It is an important fact that the 



