394 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



hydrachloride and sodium acetate, but most of the pollen grains 

 were apparently free from sugar at this stage. With Sudan II 

 and alkanin no reaction for fat was obtained. With Mill on 's 

 reagent, the pollen turned distinctly red. Tliis reaction was in- 

 terpreted as indicating the presence of proteins or amino acids. 

 When treated with ruthenium red the contents became distinctly 

 pink and were not decolored by washing. Also the walls reacted 

 slightly to ruthenium red. The pronounced reaction of the con- 

 tents with ruthenium red is likely due to amino acids. With 

 the methylene blue the walls and sometimes the contents adjacent 

 to the walls stained violet, indicating the presence of pectin. 

 Both Congo red and haemotoxylin stained the walls, thus indi- 

 cating the presence of cellulose. From the tests it appears that 

 the stored food of the pollen is present in the form of starch in 

 the young bud, but consists of proteins or amino acids, some pec- 

 tic substances, and occasionally slight traces of sugar at the 

 time of pollination. The constituents of the wall are cellulose 

 and pectic substances. 



THE WATER ABSORBING POWER OP APPLE POLLEN. 



The water absorbing power of the pollen of the five varieties 

 was found to lie in the same range of variation. Even pollen 

 from the same anther varied much in ability to absorb water. A 

 very small number of pollen grains in some samples became tur- 

 gid in 70 per cent cane sugar solution after 72 hours. Ninety 

 per cent remained plasmolyzed in 55 per cent cane sugar during 

 48 hours, while in a 35 per cent solution about 90 became turgid 

 in less than one hour and practically all within 48 hours. The 

 absorbing power of most of the pollen was, therefore, overcome 

 by the osmotic force exerted by cane sugar solutions ranging 

 from 35 to 55 per cent. Calculated according to Berkeley and 

 Hartley^ these solutions represent an osmotic force ranging 

 from 45 to 105 atmospheres. Even dead pollen showed consid- 

 erable absorbing power and when put in the weaker solutions 

 dead pollen became turgid in a short time and many burst. 

 GERMINATION OF THE! POLLEN. 



In germinating the pollen in solutions, chiefly cane sugar so^ 

 lutions were used, although other sugai's were tried and found 

 to be good. The solutions are given in percentages and were 

 made up by adding to the number of grams corresponding to the 

 desired percentage of sugar enough, water by weight to make 100 



^Physical chemistry, Phillips, J. C, p. 51. 



