Mar. II, 1918 Sterility in the Strawberry 665 



inequality of the last two classes must be due to inequality in production 

 of the two kinds of female gametes FB and Fb ; the latter, which carries 

 femaleness and narrow leaf linked, appearing less frequently than FB. 

 Apparently with the suppression or loss of the determiner for broad 

 leaves in the sex chromosome, there has also been a partial suppression 

 of a factor necessary for the normal development of male and to a less 

 extent of female gametes. In personal correspondence with Dr. ShuU 

 he informs me that there is actually a great deal of pollen sterility in 

 the narrow-leaved Lychnis male. 



CONCLUSIONS 



(i) The flowers of Fragaria are pentamerous with regard to all parts 

 except pistils. The stamens are arranged in three whorls; the outer 

 parapetalous series of 10 stamens, the middle antipetalous, short fila- 

 mented series of 5, and the inner antisepalous series of 5. Increases in 

 stamen number are due to the addition of 5, or a multiple of it, to either 

 the antipetalous or the antisepalous series. Decreases in stamen number 

 are due to the loss of first the antipetalous and next the antisepalous 

 series. Apparently the parapetalous series are permanent. Decrease 

 in stamen number is in no way related to dieciousness. 



(2) There is a positive correlation between flower position, flower part 

 number, and size of fruit in the strawberry. 



(3) The wild American species of strawberry, from which the cultivated 

 varieties have been derived, are for the most part diecious. The pistillate 

 plants bear staminodia, which rarely develop as far as the pollen mother 

 cell stage, and the staminate plants bear pistils which superficially ap- 

 pear to be perfect but which are only occasionally functional. In a few 

 wild clones of F. virginiana, which appear to be sterile, pollen develop- 

 ment is carried as far as the tetrad division or slightly beyond this to 

 the liberation of the microspores, when complete disintegration of the 

 anther contents to an oily mass takes place. In other instances a por- 

 tion of the microspores develop normally while the remainder within the 

 same anther disintegrate, while in other clones shortly after liberation, 

 and following a slight growth of the microspores, complete abortion of 

 the same type as that found in hybrids takes place. These anther types, 

 in wild clones, all appear to be various expressions of a tendency toward 

 dieciousness and are not the result of hybridization. Similar anther 

 types are common in certain cultivated varieties, on the early flowers of 

 an inflorescence, and especially on those appearing early in the season. 



(4) There is a correlation between flower position and fertility of 

 pistils, fertility decreasing in the later flowers of an inflorescence. Pistil 

 sterility is expressed in the production of irregularly shaped berries or 

 entirely sterile flowers. Sterility of the later flowers of an inflorescence 

 is more general in hermaphrodites than in pistillates, suggesting that 

 the hermaphrodites have been derived from staminates of the diecious 

 wild forms. 



