The Living Materials 45 



tions against mechanical and chemical shocks, 

 provided with very special and obscure nutrition, 

 and requiring considerable manipulation for its 

 excision. Hannig (1904, 81), Stingl (1907, 85), 

 Dietrich (1924, 79), Essenbeck u. Suessenguth 

 (1925, 80), White (1932, 89), Tukey (1933, 86, 

 1934, 87, 1938, 328), Werckmeister (1934, 88), 

 LaRue (1936, 82), LaRue and Avery (1938, 83), 

 Razdorskii (1938, 84), and others have grown ex- 

 cised embryos of more or less advanced stages of 

 development, but egg cells have apparently not 

 yet been cultured. It is probable that the difficul- 

 ties involved can be overcome. Indeed, Tukey 's 

 results with older embryos of stone-fruits indicate 

 considerable progress. However, since the culti- 

 vation of such embryos, as practiced, results in 

 entire plants which differ in no wise from plants 

 obtained from viable seed by the more usual meth- 

 ods, such cultures are likely to prove of value only 

 in special cases. Noteworthy among these are the 

 fairly numerous cases where viable embryos are 

 initiated but where, for one reason or another, 

 endosperm is not developed so that the embryos 

 die of starvation. Such was the case with Tukey 's 

 hybrid peaches (1933, 86) and with the Musa semi- 

 nifera studied by White (1928, 332). Similar 

 "physiologically sterile" plants have been re- 

 ported in the literature on numerous occasions. 



