Mar. II, i«i8 Sterility in the Strawberry 615 



Variations in stamen number from the above arrangement, if slight, 

 are usually due to the addition or loss of one or more stamens from the 

 antipetalous series. If a definite increase of five takes place, it may be 

 the result of an increase in one of two places: either the 5 single anti- 

 petalous stamens may be replaced by 5 pairs to form a whorl of 10 (fig. 2, 

 b, AP), or the 5 antisepalous stamens may have been replaced by 5 pairs 

 of parasepalous stamens located at the same points as the whorl of 5 

 (fig. 2, c, PS). A further increase in the number of antipetalous stamens 

 may consist in the development of a pair located on either side and 

 slightly inside of the single antisepalous stamens (fig. 2, d, AP). These 

 are characterized by the same short filament that is found in the anti- 



Fig. 2. — Flower diagrams of Fragaria spp., showing stamen arrangement: A.S represents antisepalous; 

 AP, antipetalous; PP, parapetalous; and PS, parasepalous stamens, a represents the 20-stamen 

 arrangement found commonly in F. vhginiana and F. americana and many cultivated varieties; 6 and c, 

 a 25-stamen arrangement found in F. virginiana and some cultivated varieties; d, a 35-stamen arrange- 

 ment sometimes found in cultivated varieties; while e and/represent a 10 and 15 stamen arrangement 

 found in some clones of F. ainericana, 



petalous whorl of 5. This increase, plus the 20-stamen arrangement, 

 gives a 30-stamen arrangement, or with either of the two 25-stamen 

 arrangements, gives 35. 



Rydberg {34, p. loY has pointed out that the antipetalous stamens which 

 appear to be the middle whorl in Fragaria spp. are truly an itmer whorl 

 which has been pushed out to form apparently a middle one (fig. 2,d), and 

 that the outer parapetalous stamens are in reality younger with regard to 

 development than the antisepalous or inner series. A study of the 

 position of the accessory stamens of the antipetalous series (which can 

 readily be distinguished by their short filament) and of the order of 

 stamen development indicates that this view is correct. 



1 Reference is made by number (italic) to "Literature cited," p. 666-669. 



