228 



The Journal of Heredity 



few of the common varieties showed 

 the following percentages of defective 

 pollen: Beauty of Hebron, 30%; Early 

 Norther, 44%; Early Rose, 60%; Green 

 Mountain, 67%; White Elephant, 58%), 

 and in a hybrid between Keeper and 

 Silverskin, 89%. When pollen is taken 

 from mature anthers and mounted in 

 lactic acid the defective grains appear 

 empty. The fact that there are empty 

 pollen coverings in the loculi indicates 

 that pollen development is stopped 

 after being liberated from the tetrad. 

 In anthers where there is complete pol- 

 len abortion at maturity the pollen 

 appears white instead of the character- 

 istic yellow. After dehiscence the an- 

 thers curve backward away from the 

 style. It would appear from the above 

 percentages, that while all of the var- 

 ieties bear considerable quantities of 

 aborted pollen, in most cases there would 

 be ample normal pollen for self or 

 cross pollination. In one collection of 

 flowers from Early Ohio and Rural 

 New Yorker there was nearly complete 

 pollen abortion. If this were generally 

 the case large fields of either of these 

 varieties would fail to set seed-balls 

 even if the flowers did not drop. 



An examination of the pistil, on the 

 other hand, shows that the ovules un- 

 dergo normal development (Fig. 19, No. 

 6) . There are evidences of disintegration 

 in some embryo sacs but on the whole 

 they appear to be undergoing the usual 

 growth up to the time they are cut off 



when the flower drops. Some of the 

 pistils are whitish in color at the base 

 instead of distinct green before the 

 flowers drop, and in those flowers which 

 drop after opening, the abscission layer 

 at the base of the style forms, and occa- 

 sionally a flower persists long enough 

 for the style to absciss. Receptive 

 stigmas have very few pollen grains on 

 them under field conditions. It often 

 happens that seed-balls develop but bear 

 few mature seeds. Apparently the stim- 

 ulus from these is sufficient to hold the 

 balls on. 



What relation then does the dropping 

 of flowers in the potato bear to the nor- 

 mal functioning of pollen and pistil? 

 Since complete abortion of pollen occurs 

 in many forms in which the pistil func- 

 tions normally, this factor is not neces- 

 sarily a cause of dropping, although 

 pollen development is carried up to the 

 liberated microspore. The pistil devel- 

 ops ovules and the stigma becomes 

 receptive in the maturest flowers which 

 shows that normal pistil development 

 takes place in flowers in which the pollen 

 is suppressed. Since the flowers are cut 

 off before the stimulation resulting from 

 pollination or fertilization takes place, 

 this factor can be eliminated. Bloom, 

 likewise, precedes any considerable stor- 

 age of food material in the tuber. It 

 appears then, that there are physiologi- 

 cal influences operating independently 

 of pollen or pistil development which 

 cause the potato flower to drop. 



Robert Louis Stevenson on Heredity 



"Our conscious years are but a mo- 

 ment in the history of the elements that 

 build us. . . . And though today I 

 am only a man of letters, either tradition 

 errs or I was present when there landed 

 at St. Andrews a French barber-surgeon 

 to tend the health and the beard of the 

 great Cardinal Beaton: I have shaken 

 a spear in the Debatable Land and 

 shouted the slogan of the Elliots; I 

 was present when a skipper, plying 

 from Dundee, smuggled Jacobites to 

 France after the '15. . . . Yes, 



parts of me have seen life, and met 

 adventures, and sometimes met them 

 well. And, away in the still cloudier 

 past, the threads that make me up can 

 be traced by fancy into the bosoms of 

 thousands and millions of ascendants: 

 Picts who rallied round Macbeth and 

 the old (and highly preferable) system 

 of descent by females, fliers from before 

 the legions of Agricola, marchers in 

 Pannonian morasses, star-gazers on 

 Chaldean plateaus." 



