388 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



flowering stage proves that the intergeneric combination is not 

 lethal in itself and that causes of the death of the embryo have to 

 be sought elsewhere. 



Similar instances of the artificial culture of hybrid embryos have 

 been recorded in various other plants. To mention a few examples, 

 J0rgensen (1928) used this method to obtain hybrids between So- 

 larium nigrum and S. luteum; Beasley (1940) between Gossypium 

 hirsutum and G. herbaceum; Skirm (1942) between some species of 

 Prunus and of Lilium; Smith (1944) between Lycopersicum esculen- 

 tum and L. peruvianum; and Sanders (1948) between several species 

 of Datura. 



When the embryo is of a rather large size, it can often be dissected 

 out with a needle while the seed is held between the fingers. With 

 smaller embryos a dissecting microscope is necessary. The excised 

 embryos are transferred into previously prepared culture bottles 

 containing a nutrient medium. Since conditions favorable for the 

 growth of the embryos are also favorable for the growth of various 

 bacteria and fungi, even a slight carelessness may cause the cultures 

 to become contaminated, resulting in death of the embryos. Suit- 

 able precautions must therefore be taken both at the time of dis- 

 section of the embryos and during their transfer to the culture 

 medium. Various chemicals are available for sterilizing the seeds, 

 and contamination of the culture room from air-borne spores may 

 be reduced either by using air filters or by spraying the tables and 

 walls with a 1 per cent solution of carbolic acid. The dissecting 

 instruments are dipped in 70 per cent alcohol and flamed. The 

 embryos, being delicate, are not treated with any solution but are 

 dropped immediately after dissection into the sterile culture me- 

 dium. 



The composition of the medium is naturally a most important 

 factor. Older embryos are largely autotrophic and usually present 

 little difficulty. The present problem, however, is to try to rear 

 embryos in younger stages of development. There are two objects 

 in view. One is that hybrid embryos frequently abort at a very 

 early stage before the differentiation of the cotyledons and, there- 

 fore, it is necessary to develop proper methods for taking care of 

 them before degeneration has commenced ; the other is the long-range 

 question of understanding the nutritional physiology of embryo 

 development, of which we have little or no knowledge up to this 

 time. 



