1 1 BIOCHEMICAL SYSTEMATICS 



study illustrates clearly the fact that in some cases a small sampling 

 may not disclose a pattern of the distribution of a substance. 



Another point of interest in the canavanine work is that cer- 

 tain large and diverse genera such as Vicia, Astragalus, and Glycine 

 contain some species with canavanine present and some without. As 

 noted in an earlier section, it is possible that those species lacking 

 canavanine have, in certain cases, lost only one enzyme, specific for a 

 single step. Therefore, two different species could have complemen- 

 tary deficiencies. Hybridization could produce individuals capable of 

 forming canavanine. Canavanine would then appear as a hybrid sub- 

 stance in such a case. More will be said later about the formation of 

 "new" substances in hybrids. 



It now appears that another newly discovered amino acid, 

 like canavanine, is restricted to the Papilionoideae of the family 

 Leguminosae. This unusual acid, which gives a brilliant scarlet color 

 with ninhydrin, was identified from Lathyrus tingitanus seeds by 

 Bell (1962). It was reported to occur in only a few of many species of 

 Lathyrus examined. We have now examined nearly 300 species in the 

 family Leguminosae for the presence of lathyrine, and the acid has 

 been detected only in several species of Lathyrus. Within the genus 

 Lathyrus this amino acid is likely to be of definite systematic utility. 



CH,CH 



\00H 



lathyrine 



Alston and Irwin (1961) have reported on the relative variation 

 in free amino acids and secondary substances in five species of Cassia. 

 They noted that, although definite differences did appear in the 

 amino acid chromatograms of different species, the extent of variation 

 was far less than that of fluorescent substances. For example, from 

 ten to twelve amino acid spots appeared, no more than nine of which 

 were present in a single species. Superimposed upon the relative 

 limitation in numbers of amino acids which are readily disclosed from 

 crude extracts is the fact that the quantities of free amino acids 

 present at a particular time tend to be quite sensitive to numerous 

 external and, presumably, internal influences, for example, light and 

 temperature, nutritional conditions, stage of development, and so on. 

 Fowden (1959) has observed that certain amino acids such as histi- 

 dine, tyrosine, cystine, and methionine are rarely detectable unless 



