EMBRYOGENESIS IN FLOWERING PLANTS 307 



developments observed by Sanders in Datura stramonium were failure 

 to grow, tissue swellings, swollen spreading cotyledons, premature 

 differentiation of roots and/or plumules, multiple and fasciated embryos, 

 and irregular bud-like growths. When the normal embryonic differen- 

 tiation has been arrested, the renewed growth proceeds from a plurality 

 of growing points. The degree of differentiation at the time of excision 

 appears to be the chief factor determining the type of growth produced 

 in culture. Initially normal embryos tend to continue to develop 

 normally in culture media; initially abnormal embryos, if they grow, 

 tend to develop abnormally. 



Normal embryos in culture in due course pass out of the embryonic 

 into the seedling phase, the attendant changes being comparable with 

 those which normally take place on seed germination. In some embryo 

 cultures, however, the growth developments in plumule, hypocotyl and 

 radicle may take place independently of one another. Sanders found 

 that root formation in Datura is favoured by medium concentrations 

 of Na(P03)n and the lower concentrations of Fe3(P04)2, and, in 

 particular, by the omission of malt. The elongation of the hypocotyl 

 increased with increased sucrose, with decreased Fe3(P04)2 and with 

 the addition of malt, but was unaffected by the Na(P03)n concentration. 

 The growth of the plumule, on the other hand, occurred more often at 

 the lower sucrose concentrations, at the higher Na(P03)n concentra- 

 tions, and with the omission of malt. These embryo culture experiments 

 thus demonstrate how different are the nutritional requirements of the 

 several organs, both quantitatively and qualitatively. In liquid culture 

 media, the normal, regulated growth of the embryo may be disturbed, 

 one or other of the organs tending to grow more rapidly or more 

 slowly according to the balance of nutrients provided. Lee (1950) has 

 shown that, in tomato seedlings, the relative growth values of the 

 individual organs are different when the organs are isolated than when 

 they form part of an intact plant, e.g. isolated cotyledons have higher 

 growth values than intact attached ones, but the reverse is true of stems 

 and roots. The factors determining these differences in relative growth 

 are probably the correlative effects of one part on another, the relative 

 availability of the substances required for growth, translocation effects, 

 and the conversion of substances during translocation. 



A DEVELOPMENTAL STUDY OF CAPSELLA 



Rijven (1952) has investigated the physiology of the embryo and 

 endosperm of Capsella during development. The embryogeny of this 

 classical species was described by Hanstein (1870) and Soueges (1916, 

 1919) Figs. 53, 54. Germination is described by Rijven as beginning 

 'at the moment that the embryonic tissue — in a state of cell division 



