POLLINATION OF THE MANGO. 11 



of densities varying from 1 to 75 per cent were tried, gelatine or 

 leached agar-agar being added to them in varying amounts. Finally, 

 it was found that the best results were obtained with a sugar solu- 

 tion of 25 per cent to which 0.5 per cent of agar-agar had been added. 

 To make this, a 50 per cent solution of cane sugar was prepared and 

 sterilized and then to 10 c. c. of this solution an equal amount of 1 

 per cent leached agar-agar 1 was added. The sugar solution was 

 made up by weight, one-half ounce of cane sugar being added to 1 

 ounce of distilled water. Before using the culture medium it was 

 sterilized and after two or three days resterilized, repeating this 

 process two or three times, after which a new solution had to be 

 prepared. 



In solutions of a density less than 20 per cent many of the pollen 

 grains burst within a few minutes, as they do in water, and in solu- 

 tions of a greater density than 30 per cent no germination took place. 



The effect of temperature upon the germination of the pollen 

 appeared to be of the greatest importance, and many failures during 

 the early part of the work, when the nights were cold, can probably 

 be attributed to this cause. 2 Later in the season a few experiments 

 were made to determine the minimum temperature at which germi- 

 nation would take place. Cultures were made as usual, six of one 

 variety, and three of them placed in the ice box, the other three in 

 the moist chamber at room temperature as a check. The result was 

 that no germination took place at 55° F.; at 60° F. there appeared 

 to be a feeble germination of a few grains; at 65° F. the germination 

 was a little better, but still below normal. The best results were 

 obtained between 75° and 80° F., nearer 80° than 75°. No cul- 

 tures were tried in a temperature above 80° F., which was the highest 

 reached in the moist chamber kept in the laboratory. It seems 

 doubtful whether mango pollen can be expected to germinate nor- 

 mally at a temperature below 60° F. 



As to the time required for germination, numerous cultures were 

 examined at the end of 30 minutes, 1 hour, 2 hours, and so on, with 

 the result that at a temperature of 76° F. the first signs of germi- 

 nation were visible within 1 hour. At the end of this time the tubes 

 had not yet reached a length equal to the diameter of the pollen grain, 

 but at the end of 2 hours and 15 minutes the longest pollen tubes were 

 in length almost twice the diameter of the pollen grain. In order 

 to give the pollen tubes time to develop to as great a length as pos- 

 sible, most of the cultures were allowed to remain 12 to 24 hours 

 before examination; at the end of this time development seemed to 



1 This material was obtained from Dr. Albert Mann. 



« The failure of McMurran to germinate' mango pollen (McMurran, S. M., The anthracnose of the mango 

 in Florida, U. S. Dept. Agr. Bui. 52, 15 p., 4 fig., 4 pi., 1914) may have been due to cold weather at the 

 time the attempt was made. 



