304 EMBRYOGENESIS IN PLANTS 



The best root and shoot growth was obtained in a medium containing 

 0-2-6-0 per cent sucrose. 



Utilisation of Nitrogen Compounds. A knowledge of the forms in 

 which nitrogen can be utiHsed by embryos of different ages is of 

 paramount importance. Spoerl (1948) has pointed out that although 

 most embryos in situ probably receive and utilise nitrogen in an organic 

 form, comparatively little is known of the effect of such substances on 

 the growth of embryos in culture. Accordingly, he used various amino 

 acids as sources of nitrogen in the culture of orchid embryos, cultures 

 supplied with ammonium nitrate and others with no nitrogen affording 

 a basis for comparison. Orchid seeds, both immature and mature, are 

 useful for such studies since the germ is small and undifferentiated and 

 the seed devoid of storage materials. Of some nineteen aminoacids 

 tested, most were found to act as inhibitors to normal embryo develop- 

 ment; and none yielded as good growth as ammonium nitrate. 

 Arginine was the only aminoacid which supported good growth in 

 young embryos, all the others tested having an inhibitive effect under 

 the experimental conditions. With older embryos, aspartic acid proved 

 a good nitrogen source, but glutamic acid neither supported good 

 growth nor inhibited it. Growth in the light was significantly better 

 than in the dark with several of the nitrogen sources and also when no 

 nitrogen was supplied. Cysteine and cystine, however, gave better 

 growth in the dark. These experimental results show that little of the 

 nitrogen of the aminoacids is as effectively utilisable by the growing 

 embryo as is that of ammonium nitrate. 



Other studies of aminoacid utilisation by species from different 

 systematic groups show little consistency in the results obtained. Thus 

 Burgeff (1936) and Withner (1942) found no stimulation of growth of 

 orchid embryos on the addition of individual aminoacids, or mixtures 

 of aminoacids, to a medium already supplying inorganic nitrogen. 

 Knudson (1932) found several of these acids to be inadequate nitrogen 

 sources for embryo growth. Brown (1906), however, reported that 

 asparagine, aspartic acid, and glutamic acid gave increases equal to 

 that from potassium nitrate in dry weight of excised barley embryos. 

 Klein (1930) states that aminoacids are absorbed by plants under 

 sterile conditions, but are not equally utilisable; and Virtanen and 

 Linkola (1946) have found that aspartic and glutamic acids are used 

 especially well by pea and clover plants, but these acids cause a loss of 

 dry weight in wheat and barley plants. MacVicar and Burris (1947) 

 have reported that very good growth of clover plants was obtained with 

 asparagine, glutamine, arginine and glycine. Among moderately good 

 sources of nitrogen were alanine, histidine, cystine, glutamic acid and 

 urea, whereas norleucine, methionine, tyrosine, leucine, tryptophane 



