306 EMBRYOGENESIS IN PLANTS 



developed into dwarf plants. Lammerts (1942) obtained similar results 

 with apricot, peach, cherry, rose and camellia. 



In Tukey's experiments, each size of embryo that could be grown in 

 culture yielded a characteristic growth pattern, this being comparable 

 with the 'juvenile' and 'adult' forms known in other plants. This seems 

 to confirm Goebel's view that organisms are constantly changing 

 throughout their ontogenetic development, and that the genetical 

 constitution of a plant alone does not determine morphogenesis and 

 functional activity. Tukey observed that embryos in culture do not 

 pass through the morphological stages characteristic of those within 

 the seed ; instead, they enter at once into an independent development 

 characteristic of the age of the embryo when excised. The younger the 

 embryo is on excision, the more abnormal is its growth behaviour; 

 and the older the embryo is on excision, the less easily is it upset by the 

 new environment. Embryos at different stages of development have 

 different requirements: a liquid medium is favourable at one stage of 

 development and not at another; and glucose is favourable at one stage 

 and inhibiting at another. Even mature seeds must be after-ripened 

 before they develop normally. These facts indicate that both internal 

 and external factors must be considered. The failure of embryos to 

 follow the 'normal' pattern of embryonic development outside the 

 embryo sac raises the question as to the nature of the environment 

 which brings about 'normal' development. Hannig (1904) and others 

 have shown that the shape of the embryo is altered by the surrounding 

 tissue. 



Using self and hybrid embryos of Datura discolor, D. inoxia, 

 D. metel a.nd D. stramonium, the embryos where possible being excised at 

 the heart-shaped stage, Sanders (1950) studied the effects of different 

 concentrations of sucrose, Na(P03)n and Fe3(P04)2 and filtered malt 

 extract in the culture medium. It was observed that the vigour and type 

 of embryonic growth were determined primarily by the size of the 

 embryo at excision, this being especially marked in the response to 

 sucrose. The effect of the genetical constitution was indicated by the 

 fact that the growth of D. stramonium with 4-0 per cent sucrose was 

 42 times that with 0-5 per cent, whereas embryos of the other three 

 species only increased from 1-2 to 1-7 times over the same range. Some 

 other specific differences were also observed in relation to the concen- 

 tration of Na(P03)n in the medium. With regard to growth values, 

 hybrid embryos resembled one or both parents, were intermediate 

 between them, or, occasionally, were unlike either parent. Reciprocal 

 hybrids were usually similar. 



Embryo development in artificial culture media may follow normal 

 or abnormal paths in different circumstances. Among abnormal 



