POLLINATION OF THE MANGO. 9 



removed entirely. There was no appreciable difference between the 

 covered and the uncovered sides of the tree in the number of fruits 

 produced. 



THE POLLEN. 

 SHAPE AND CHARACTERISTICS OF THE POLLEN GRAIN. 



In its normal dry state the pollen of all varieties examined exhibited 

 an oblong-oval form, slightly broader in some varieties and narrower 

 in others, but approximating the same shape in all. ■ When mois- 

 tened by being placed in water the grains immediately swell and in 

 a very few seconds have become spherical in outline, but on being 

 allowed to dry out they resume their oblong-oval form. Under the 

 microscope the dry pollen grains exhibit one or two sutures extending 

 longitudinally; these disappear when the grain is moistened and 

 swells: The thick outer membrane, or extine, is rugose on the sur- 

 face and contains four pores, through one of which germination takes 

 place. These pores frequently show very plainly after the pollen 

 grains have been in a culture medium for 24 hours, the intine often 

 protruding slightly from each of them. There are slight differences 

 in the form of the ungerminated pollen grains of different varieties 

 after they have been left for several hours in the culture medium;, 

 thus, it was noted that in some varieties the ungerminated grains 

 commonly assumed a distinctly triangular outline, those of another 

 variety were almost spherical, while those of still another were slightly 

 oblate in form. 



NUMBER OF POLLEN GRAINS PRODUCED BY THE ANTHERS. 



The greatest variation was found in the number of pollen grains 

 produced by the anthers, not only among different varieties but in 

 different anthers from the same tree. The smallest number was 

 found in the anthers of the No. 11 seedlings examined at the Royal 

 Palm Nurseries, Oneco, Fla. The trees were just coming into bloom 

 after rather cold weather, and the flowers did not appear to be strong. 

 The anthers were in many cases rather weakly developed and con- 

 tained only 35 to 100 pollen grains, 200 being the largest number 

 counted. Later in the season more than 400 grains were counted in 

 anthers from other trees of this same race. The highest number 

 counted was about 1,200, in the anthers of the Mullgoa (not Mulgoba), 

 a variety in which staminate flowers greatly predominate and which 

 produces more pollen than many others. An average number of 

 pollen grains probably could be established for each variety and 

 would be found to vary considerably in different varieties, some 

 averaging not more than 400 or 500, while others certainly would go 

 as high as 700 or 800. 



84444°— Bull. 542—17 2 



