Dec, 1921] PATON — POLLEN AND POLLEN ENZYMES 479 



substances, and callose. Sometimes one, or more than one, of the four 

 materials are present in the same grain. These substances are indicated 

 by characteristic solubility tests and by color reactions. He examined the 

 pollen of 19 species of monocotyledons and 26 species of dicotyledons. His 

 plates give over a hundred illustrations of the pollen grain coats and their 

 sculpturing, showing details brought out by staining methods and chemical 

 treatment. Mangin (1888, p. 144) states that the membrane is formed of 

 pectin. 



Water makes up a large but variable part of the grain. Thus Koessler 

 (1918, p. 420) found 10.5 percent of moisture in ragweed pollen, while Heyl 

 (191 7, p. 1470) reports 5.2 percent for the same kind of pollen. Braconnot 

 (1829, p. 104) found 47 percent of water in cat-tail pollen. Lidforss (1899, 

 p. 292) examined a number of species and found the average moisture 

 content to be about 10 percent. 



The colors of pollen differ greatly. It is deep yellow in Easter lily, 

 dark red in tiger lily, salmon in cypress, and white in petunia. Even in 

 the same flower the color may vary, as is noted by Plimmer (1912, p. 51) 

 in Lythrum salicaria, which has yellow pollen in the short stamens and 

 bluish green pollen in the long stamens. Heyl (1919 b, p. 1285) states that 

 the yellow pigment of ragweed is entirely glucosidic and about 0.6 percent 

 of the pollen. He finds a quercitin glucoside which on melting yields a 

 cherry-red oil; and a glucoside isorhamnetin which has beautiful character- 

 istic crystals in the form of hexagonal prisms. So far, no other analysis 

 of the pigments of pollen has been located in the literature. 



Starch has been found present in some kinds of pollen and absent in 

 others. Molisch tested no varieties and found starch abundant in 45, 

 only a trace in 9 varieties, and absent from 46. That is, about half the 

 kinds tested contained starch. Lidfoiss (1899, pp. 294-298) examined 150 

 wind-pollinated flowers of 72 genera and 29 families of native or naturalized 

 Scandinavian plants, and found the pollen of all rich in starch. On the 

 other hand, he tested the pollens of a few wind-pollinated tropical plants 

 and found them starch-free. He also calls attention to the fact that Na^eli 

 found the pollens of Alnus glutinosa and Plantago lanceolata, collected in 

 Germany, starch-free, while pollens of the same species collected by himself 

 in a more northerly region contained starch. Similarly, Nageli found the 

 pollen of juniper on Swedish mountains to be rich in starch, while Molisch 

 found little in that of the Austrian juniper. Further, Molisch states that 

 the pollen of Antirrhinum tortuosum is completely starch-free in summer, 

 but in November he finds grains of three sorts, those which are normal but 

 starch-free, little empty grains, and normal starch-containing grains. 

 Tischler (1909, pp. 219-242), however, does not find this correlation between 

 climate, or temperature, and the starch content of pollen. He examined a 

 large number of tropical plants at Buitenzorg and reports that the plants 

 growing under relatively unfavorable conditions of assimilation, for example 



