FORMATION OF OILS AND PROTEINS 43 



properties of leaf starch have been described by Spoehr and Milner (1935, 

 1936). 



Grafe and Vouk (1912, 1913) and Melchior (1924) found that in some 

 plants inulin replaces starch. Inulin is a polymer oi fructose, constructed 

 from fructofuranose units, in the same way that starch is built up from 

 glucopyranose units. Varied reserve materials are encountered in algae. 

 Starch is found in green and red algae {Chlorophyceae and Rhodophyceae) ; 

 and glycogen (a form of starch common in animals) in blue-green algae 

 (Cyanophyceae). Brown algae (Phaeophyceae) store pentosans and 

 fucosans. 



2. The Photosynthetic Formation of Oils and Proteins 



All storage materials mentioned so far were carbohydrates. How- 

 ever, many algae, particularly the diatoms {Bacillariophyceae), but also 

 some green algae (Vaucheria), store oils or fats instead of carbohydrates 

 (Beijerinck 1904). In addition, the chromoplasts of most algae contain 

 so-called pyrenoids, peculiarly shaped bodies (c/. page 357), usually con- 

 sidered as masses of reserve proteins surrounded by starch sheaths. 



It has sometimes been suggested that these reserve materials may 

 represent the direct products of photosynthesis in algae. Bond (1932) 

 thought for example that diatoms may produce fats directly by photo- 

 synthesis, according to the equation: 



light 



(3.5) 55 CO2 + 52 H2O > C66Hio40« + 78 O2 



However, we have seen (page 34) that the photosynthetic quotient of 

 an oil-storing diatom was found to be not larger than 1.05, while equatoin 

 (3.5) would require a value of 1.42. Thus, the oil deposits of the diatoms 

 — and probably the fat and protein stores of other algae as well — must 

 be considered as products of comparatively slow secondary transforma- 

 tions not directly associated with photosynthesis. 



Oily drops have been observed not only in algae, but also in the 

 leaves of some higher plants. Briosi (1873) suggested that these drops 

 are produced directly by photosynthesis; however, his conclusions were 

 criticized by Holle (1877) and Godlewski (1877). 



Meyer (1917) observed, in illuminated leaves of Tropaeolum majus 

 the temporary formation of what he described as ''droplets of an assimi- 

 latory secretion." Later (1918) he suggested that oil drops formed in 

 some green algae (e. g., Vaucheria terrestra) are of a similar nature, and 

 proposed that this " assimilatory secretion" be considered as an immedi- 

 ate product of photosynthesis. From observations of its chemical 

 behavior (1917^), he concluded that it is not a fat, but may possibly 

 consist of hexenaldehyde, a compound whose presence in green leaves 



