EMBRYOGENESIS IN FLOWERING PLANTS 



309 



development in that it marlcs the transition from the initial radial 

 symmetry to the bilateral symmetry that become apparent with the 

 formation of the cotyledons. This change in symmetry is attributed by 

 Rijven to induction by bilaterally disposed gradients in the ovular 

 environment. Certainly some in vitro embryos did not lose their radial 



stage m to W 



Stage YioMI 



Fig. 83. Capsella biirsa-pastoris 

 Diagrammatic representation of embryo development; see Text (after Rijven). 



symmetry and developed as many as six cotyledons, a result like that 

 obtained by Overbeek, Conklin and Blakeslee (1942) using Datura 

 embryos. Failure to grow very young embryos indicates that certain 

 ingredients are lacking in the synthetic culture medium or that certain 

 refinements have not yet been achieved. Embryos at the torpedo stage 

 grow well in culture. The osmotic value of the culture medium (or 

 embryo sac sap) is an important factor in determining the nature of the 

 embryonic growth. 



Sucrose proved to be the best source of carbohydrate for embryo 

 growth in pure culture. Casein-hydrolysate strongly promoted growth. 

 Glutamine was the outstanding aminoacid for use in culture media for 



