POLLEN AND PISTILS OF APPLES 



391 



cytoplasm and some bursting after a few hours, wihile on the 

 membranes the tubes of the same age were normal in appear- 

 ance. The membranes were found suitably dried when the sur- 

 face moisture was removed and tliis was accomplished by press- 

 ing them once between blotters. 



The longest tubes obtained in any of the sugar solutions and 

 on the membranes were about 2 mdllimeters. This limit in growth 

 was attributed to the exhaustion of stored food in the pollen 

 grain, and since no more growth was made in the sugar solution 

 than on the membrane, it was again evident that the pollen tubes 

 did not use the sugar as a food. Even when grown on membranes 

 soaked in sugar solutions, thus eliminating the feature of poor 

 aeration, the tubes were no longer than on membranes soaked in 

 distilled water. It is evident from the behavior of the pollen in 

 water, in the sugar solutions, and on the moist membranes that 

 germination depends only upon a water supply. This water re- 

 quirement is a little less than the amount of water absorbed when 

 the pollen is in pure water, as is shown by the fact that the larg- 

 est percentage of germination was obtained in the least time in 

 2^ per cent cane sugar solution and on membranes. In stronger 

 sugar solutions the pollen, although germinating very little in 2 

 hours, gradually took up water until the required amount was 

 obtained and then germinated, thus often showing a fair per 

 Cfiut of germination at the end of a long period. In table IV are 

 shown the comparative rates of germination in the different per 

 cents of sugar solution. 



TABLE IV. 



THE PERCENTAGES OF GERMINATION AND LENGTHS OF TLTBES 



OBTAINED IN THE SAME SOLUTIONS WITH TI.\]1<] 



PERIODS OF DIFFERENT LENGTHS. 



