Mar. II, 1918 Sterility in the Strawberry 619 



or to the formation of the tetrads when degeneration occurs. This be- 

 comes apparent first through degeneration of the mother-cell wall and 

 the cytoplasm, if the homoeotypic division is taking place, leaving the 

 spindles and chromosomes standing out sharply in this degenerate mass; 

 or if the tetrads have already been formed, the material in which the 

 microspores are embedded disintegrates and is follov/ed directly by the 

 disintegration of the microspores. Plate 36, E, shows degenerating 

 tetrads; F shows a later stage of the same thing in which the micro- 

 spores have completely degenerated; and G shows the condition found 

 in mature anthers of this type. 



Occasionally development may proceed to the formation and libera- 

 tion of the microspore when, following a slight thickening of the walls, 

 degeneration of the contents and disintegration of the microspore walls 

 takes place. The same type of degeneration is found here as where 

 earlier abortion takes place. The walls become thickened and, as degen- 

 eration proceeds, show a beaded appearance and finally break up into 

 drops of a yellow oily appearing substance which makes up the mass 

 shown in figure G (PI. 36) . In other clones of F. virginiana development 

 proceeds to the liberation of the microspores from the tetrad when, fol- 

 lowing a slight development of the microspore wall, degeneration of the 

 cell contents takes place, leaving aborted pollen of the type so charac- 

 teristic of hybrids. 



In the cultivated hermaphroditic varieties which produce staminodia 

 on the early primary flowers (Pi. 36, D, G), and on some other varieties, 

 such as Lovett, Glen Mary, and Minnesota 1017 X Progressive 9-24 (PI. 36, 

 B, E), these same types of anthers characterized by being small, shrunken, 

 and bleached yellow or deep ocher are common. They show both types 

 of degeneration — i. e., complete disintegration of the anther contents 

 and abortion of the microspore contents following their liberation from 

 the tetrad. Figure H, Plate 36, shows a section of a whitish yellow 

 anther of the type shown in figure 3, 8 and 9, from a primary flower of 

 Minnesota 3, a variety which for the most part produces normal stamens. 



Jeffrey and others have recently given emphasis to the relationship 

 between aborted pollen and hybridity and have attempted to correlate 

 any considerable amount of pollen abortion with a hybrid condition of 

 the plant. Apparently in the strawberry the above type of pollen 

 sterility and the tendency toward dieciousness are very closely related. 

 As all degrees of stamen development may be found on a single culti- 

 vated variety of the strawberry, and on some wild plants also, from the 

 small staminodia to well-developed stamens bearing normal pollen, it 

 seems safe to conclude that these intermediate stamen types bearing 100 

 per cent aborted pollen and found in apparently pure F. virginiana are 

 not the result of hybridization but are' really the expression of various 

 degrees of dieciousness. 



Whether the clones of F. virginiana bearing these intermediate anther 

 types are able to develop fruit, thus indicating whether they have been 



