Mar. ir. 1918 Sterility in the Strawberry 655 



absorbing liquids when placed in them, and so the grains of the type 

 shown in Plate E, figure 13, are likely to cause inaccuracies when the ordi- 

 nary methods of determining the percentage of good and abortive pollen 

 are employed. 



It seems clear thus far that degeneration of the microspores and pollen 

 grains is a phenomenon closely related to the very active metabolic proc- 

 esses which are taking place during this period of the plant's life history. 



DISCUSSION OF RESULTS 



T"hus far there has been shown to exist in the strawberry types of 

 sterility due to at least two distinct causes. 



In some of the wild species, including F. elatior, F. platypeiala, F. 

 cuneifolia, and F. chiloensis, it seems highly probable that the species 

 are diecious, while F. virginiana is unquestionably so for the most part. 

 Dieciousness is expressed in the production of pistillate plants bearing 

 staminodia, which, so far as I have observed, never produce pollen. 

 The staminate plants bear normal stamens and pistils, which appear 

 normal but which seldom are fertile. Certain types are also found which 

 are intermediate between these two types. A few staminate plants may 

 bear fruit on one or more of the early flowers. These flowers may or 

 may not bear stamens, but both staminodia and intermediate anthers 

 are found on them. Other plants which are apparently staminate 

 develop only intermediate anthers in which abortion takes place at the 

 tetrad division or shortly after, resulting in a degenerate mass in the 

 anther. Another staminate type has recently been studied which bears 

 fruit on the primary and occasionally on some of the other flowers. 

 The anthers of the primary flowers are reduced to staminodia. The 

 secondary flowers carry pollen development through to the liberation 

 of the microspores when 40 to 80 per cent of them abort and degenerate 

 completely, forming a yellow oily mass. The remaining grains develop 

 normally and are fertile. These types are all found in plants of pure F. 

 ■virginiana and represent varying degrees of expression of dieciousness. 



The diecious condition of the wild species from which the cultivated 

 forms have been derived probably explains the greater sterility of the 

 later flowers of the cultivated hermaphroditic varieties, than is found 

 in those of the pistillates ; if we can accept the origin of the hermaphro- 

 dites as being from males which have developed partial fertility of the 

 female organs. The appearance of staminodia showing varying degrees 

 of development in the cultivated varieties is also the direct result of 

 dieciousness, while the intermediate types of anthers in the cultivated 

 forms are of the same nature as those found in wild staminate clones. 

 It is an interesting fact, in connection with the problem of sex deter- 

 mination and dieciousness, that where intermediate anthers or stami- 

 noids occur, either on wild clones or cultivated varieties which are able 



