EMBRYOGENESIS IN FLOWERING PLANTS 305 



and phenylalanine were poor sources, some producing severe toxic 

 effects. 



Sanders and Burkholder (1948) have reported the successful culture 

 of excised Datura embryos to healthy seedlings on nutrients containing 

 only inorganic salts and sucrose. Development was slower in culture 

 than in the seed and premature differentiation of roots and shoots 

 occurred. Various organic compounds were found to stimulate embryo 

 growth and retard premature differentiation. When casein hydrolysate 

 with cysteine and tryptophane, mixtures of aminoacids, or single amino- 

 acids, were added to nutrient solutions for embryos {±_ 0-2 mm. in 

 length) of D. inoxia and D. stramonium, the best growth was obtained 

 with casein hydrolysate plus cysteine and tryptophane, and with a 

 mixture of aminoacids approximating to the composition of casein 

 hydrolysate. The experimental results indicate that there are inter- 

 actions of the acids in their effect upon embryo growth. Whereas some 

 aminoacids were stimulatory, others were inhibitory. Moreover, the 

 embryos of the two species responded differently to individual amino- 

 acids. These investigators suggest that aminoacids are probably 

 important in the growth and differentiation of plant embryos and 

 possibly in such phenomena as seed dormancy and the crossability of 

 species. 



MODIFIED ONTOGENETIC PATTERNS 



When cuhuring excised immature embryos of deciduous fruits, 

 Tukey (1937) observed that the ontogenetic growth pattern was modified 

 in a definite and characteristic manner. Instead of following the usual 

 path of embryonic development, cultured embryos grew into plantlets 

 which exhibited a definite conformation, or growth pattern, this being 

 apparently related to the age of each embryo when excised. The normal 

 progressive morphological development of the embryo should not, 

 therefore, be regarded as an inevitable recapitulation of ancestral 

 history but as the necessary result of factors in the embryonic environ- 

 ment. Mature, or nearly mature, embryos may also produce unusual 

 types of growth, but these are unlike those obtained from very young 

 embryos. Mature but non-after-ripened seeds of Rhodotypos kerrioides 

 yielded plants with a dwarfish appearance, with short stocky hypocotyls 

 and internodes, and small dark green leaves (Flemion, 1933); this 

 investigator also reported a similar type of growth for non-after- 

 ripening embryos of peach, apple and hawthorn. Davidson (1934, 

 1935) described all plants raised in culture from immature peach 

 embryos as abnormal and dwarfish, with small, wrinkled and peculiarly 

 curled leaves. Von Veh (1936) found that seedlings of apple, pear, 

 quince, plum and cherry, raised from non-after-ripened embryos, 



