1 36 BIOCHEMICAL SYSTEMATICS 



the families Solanaceae and Leguminosae form starch in large amounts 

 are not of great value in themselves. Blackman also discussed the 

 monumental work on starch grains by Reichert (1919) which had 

 appeared shortly before and which will be discussed in a later chapter. 

 In his comparative study of starch grains, Reichert exposed numerous 

 possibilities for the use of starch characters in systematics. 



Carbohydrates are so diverse that one cannot relegate them 

 in toto to the general categories of either basic metabolites or sec- 

 ondary constituents. Not only simple hexose sugars such as glucose 

 and fructose but also the more recently familiar sugars such as ribose 

 and sedoheptulose must now be considered as basic metabolites. In 

 contrast, the sugars that represent the glycosidic portion of such 

 secondary substances as pteridines, steroids, flavonoids, cyanogenetic 

 principles, some oligo- and polysaccharides, and sugar derivatives 

 such as the sugar alcohols, are collectively more properly considered 

 as secondary products of metabolism. 



Previously, it was stated that secondary constituents 

 promise generally to be more useful than basic metabolites in sys- 

 tematic investigations. However, a basic metabolite, sedoheptulose, 

 once considered to be restricted in occurrence to the family Crassul- 

 aceae, is now found in a number of other families (in the free, non- 

 phosphorylated state). Since free sedoheptulose has a restricted 

 distribution, it is potentially systematically useful. The previous gen- 

 eralization concerning basic metabolites is supported, however, as 

 most of the simple sugars which are involved principally in energy 

 relationships, for example, glucose, fructose, maltose, sucrose, and 

 others are so widespread that they can hardly be expected to have a 

 phyletically meaningful distribution. Some sugars and sugar deriva- 

 tives which appear to be quite restricted in their occurrence may 

 actually have a much broader distribution than expected. As in the 

 case of sedoheptulose, screening of large numbers of species is neces- 

 sary to expose meaningful patterns. 



Probably many more simple sugars (up to the oligosaccharide 

 level of complexity) and sugar derivatives exist than is generally 

 appreciated. Because of the lack of any integrated treatment and the 

 encyclopedic effort required to bring together data on all the different 

 substances described to date, the present treatment is necessarily in- 

 complete. An excellent review of the carbohydrate literature is 

 available (Shafizadeh and Wolfrom, 1958). In the following brief 

 account, the main purpose is to identify some of the lesser known 

 sugars and sugar derivatives to illustrate further opportunities for 

 phytochemical systematic investigations. In appropriate situations. 



