Jane i6, 1919 Relation of Weather to Fruitfulness in PIu?n 113 



in some varieties of P. americana, pollen may almost completely dis- 

 appear from the anther during a wind, undoubtedly due to drying and 

 shaking the first day, or even the first few hours after opening. Wind 

 pollination would be more effective in these varieties than in the others, 

 although it is probable that it would be insufficient because plum pollen 

 has no appendages as in Pinus spp. to give it greater carrying capacity. 



The importance of the rapid closing of anthers upon coming in contact 

 with water, together with the fact that they remain closed as long as they 

 are wet, needs emphasis in this connection. It will be e\ddent that 

 pollination is impossible when the anthers are closed. Furthermore, 

 the conditions whiph close anthers in most cases also prevent insect 

 flight, but, even if insects were working, pollination could not take place 

 for the reason that pollen is not available. It appears, therefore, that 

 too much emphasis has been placed upon the action of rain in washing 

 pollen away because anthers close quickly enough largely to prevent it. 



RAIN INJURY TO PLUM POLLEN 



It has been shown above that anthers take up water in sufficient quan- 

 tities to close them before there is complete loss of pollen. Accompany- 

 ing the drying process which takes place in the anther and the disap- 

 pearance of the anther sap, there is a similar drying in the pollen. Before 

 dispersal, pollen changes from the typical spherical shape to one distinctly 

 oblong, and deep folds appear at the sutures. When subjected to drying 

 immediately after removal from the anther, this change in shape takes 

 place in 5 to 10 minutes and is quickly reversible in 3 to 5 minutes when 

 placed in water. With these changes in mind, the question arises as to 

 the effect of a prolonged rain upon pollen. 



The rainy period at blooming time in 191 5 started with a trace on 

 April 24 and ended with rain all day on April 26 and 27. The hea\'iest 

 rain, accompanied by a moderate wind, fell on April 26. During the 

 period of the rain there was a relatively high temperature ranging from 

 58° to 62° F. 



Following the usual cytological procedure, before drying, there were 

 fixed in Flemming's medium anthers from 48 hybrids and varieties after 

 the rain of April 26 and from 30 others after the rain of April 27. In 

 all, pollen was collected from 63 crosses and 13 varieties, representing 6 

 species, namely, Prunus americana, P. Besseyi, P. nigra, P. triflora, P. 

 pissardi, and P. cerasus. 



It would appear that this material would furnish conclusive evidence as 

 to whether or not plum pollen is burst by rain, as is held by Hedrick (8) 

 and generally by fruit growers. A careful examination of mounted 

 sections from each lot fixed as mentioned above, showed (i) that the 

 pollen was not burst and had every appearance of being normal; (2) 

 that only an occasional anther was devoid of pollen, although most of the 

 sutures were broken; and (j) there was no apparent difference in the 

 pollen condition of the different species. 

 108123°— 19 3 



