Mar. II, 191S 



Sterility in the Strawberry 



637 



degeneration can be discovered by a superficial examination. The 

 possibility of this being the case will be shown later. Nevertheless the 

 factors causing a relatively high degree of pollen abortion in apparently 

 pure species have been so little studied that to assign hybridity as the 

 only cause is, to say the least, presumptive. 



Table IX. — Variation in percentage of pollen abortion in anthers from one flower of 



Seedling yjS 



Stamen position. 



Parapetalous. 



Antipetal- 

 ous. 



29.18 

 50.00 

 41.70 

 34.61 



33-65 

 38.65 

 17.09 



Antisepal- 

 ous. 



27. 27 

 41.87 



POLLEN GERMINATION TESTS 



In view of the possibility of many of the apparently normal grains 

 being in reality abortive, attempts were made to determine the exact 

 amount of fertile pollen without regard to its apparent morphological 

 condition. The usual method of pollen germination in Van Tieghem 

 cells was employed. The results were disappointing, so far as a deter- 

 mination of actual condition of individual grains was concerned; but 

 nevertheless some suggestive conclusions may be drawn from them. In 

 all, 450 tests were made, comprising 28 of F. americana, 45 of F. virginiana, 

 and 377 of cultivated varieties. The results obtained under carefully 

 controlled conditions were very erratic. Solutions of cane sugar in 

 distilled water were used in concentrations var}dng from 7 to 60 per cent. 

 Pollen germinated to a very slight degree at both of these extremes, 

 but the optimum concentration ranged between 35 and 45 per cent. 



Temperature is an important factor in pollen germination, since at 

 ordinary room temperature there was practically no germination, while 

 if the cultures were placed in a warmer portion of the room, at a tempera- 

 ture of about 90° F. sometimes a high germination resulted. Other 

 tests, carried on under as nearly identical conditions as possible, often 

 gave entirely negative results. Tests made in an electric oven, at 95° F., 

 showed at times a high percentage of germination, while at others the 

 germination was very low. Although the proper conditions for germi- 

 nation could not always be produced, yet enough evidence was obtained 

 to conclude that wherever any normal pollen is present, a portion of 

 it is likely to have the power of germination, for in several cases where 

 over 95 per cent of the pollen was abortive some of the morphologically 

 perfect grains produced normal tubes. 



