150 BIOCHEMICAL SYSTEMATICS 



that such criteria would break down in an extensive survey of species. 

 There is no doubt that a basic problem in biochemical systematics in- 

 volves the need for greater insight in the appraisal of biochemical 

 data. The obvious fact is that some differences are apt to be more im- 

 portant than others. 



There is an interesting paper, again involving the grass family, 

 by Belval and de Cugnac (1941) concerning "glucides" of Bromus and 

 Festuca. These glucides appear to be oligo- or polysaccharide in 

 nature. The type which is characteristic of Festuca is phlein, found 

 in several other grasses including Phleum pratense. Phlein is a fructo- 

 san, hence related to inulin. However, unlike the inulin fructosans 

 which represent 2, 1' glycosidic linkages, the phlein type possesses 2, 

 6' linkages. Fructosans are laevorotatory. Belval and de Cugnac 

 found that the specific optical rotation, (an), of the fructosan from 

 Festuca species, before and after acid hydrolysis, was —49 and —96° 

 while that of Bromus species was —37 and —84°. These values were 

 said to be quite consistent within the genus. 



One questionable taxon, Bromus (or Festuca) gigantea, was 

 particularly interesting. This species has a glucide with the optical 

 rotation characteristic of Festuca. Lolium perenne and L. multi- 

 florum, which contain phlein, cross with Festuca, and the authors 

 suggest that the questionable taxon should be expected to cross with 

 certain Festuca species although it was not possible to cross it with 

 the two morphologically similar species, Bromus asper and B. erectus. 

 The authors also imply that it might also cross with Lolium. It is 

 pertinent to note that practically the entire argument in this case 

 rests upon the biochemical data. In Hubbard (1954) it is noted that 

 Festuca gigantea hybridizes with F. pratense and F. arundinacea, 

 and sterile hybrids may be obtained with Lolium perenne. 



Natural hybrids of Festuca gigantea and other species of 

 Festuca as well as Lolium were known well before the Belval and de 

 Cugnac paper (for example, Jenkins, 1933). However, there was no 

 indication that the authors were aware of the work, and in principle 

 it does not detract from the significance of the biochemical data. 



Polysaccharides 



This class of substances is referred to generally as the glyco- 

 sans. Glycosans may be composed of pentoses (pentosans) or hexoses 

 (hexosans) or even mixtures of these. In general, if a single sugar 

 predominates in the glycosan the name is derived from the sugar in- 

 volved. Although a rather large number of plant gums and mucilages 



