Mar. II, 1918 Sterility in the Strawberry 629 



fairly permanent mount if handled carefully. The lactic acid has the 

 advantage over water or alcoliol for this purpose, as it is not volatile 

 and seldom, if ever, breaks the pollen grains through osmotic pressure. 

 It readily enters and expands the normal grains, while it leaves the 

 aborted ones collapsed. It has another very distinct advantage over 

 the more mobile liquids, in that its viscosity holds both the normal and 

 aborted grains in place until the cover has settled firmly, while, if water 

 is used, the empty grains have a decided tendency to wander toward 

 the edge of the cover slide, thus invalidating the count. Where no 

 aborted pollen was present, of course no actual counts were made; but 

 where present, counts were made varying from 200 to 2,000, the object 

 in each case being to include enough grains to indicate within a close 

 range the percentage of abortion. A record was kept of the position 

 on the inflorescence of the flower from which the pollen was collected 

 in order to determine whether a similar relationship existed between 

 flower position and abortion of pollen as was found to exist between 

 flower position and stamen type in certain clones. 



The results of the pollen counts on 223 flowers of F. virginiana are 

 shown in Table V. They indicate that F. virginiana produces for the 

 most part morphologically perfect pollen, although a few plants were 

 found in which the percentage of aborted grains was high. If pollen 

 condition may be taken as a criterion of species' purity it may be said 

 that F. virginiana in this region is nearly a pure form. The appearance 

 of considerable amounts of aborted pollen in a few plants might be 

 considered as the results of the "conditions" under which these plants 

 have been grown, but the fact that several flower types have been found 

 in the wild may indicate that abortion is due to a condition arising 

 from a slight degree of hybridity consequent on the intercrossing of 

 these forms. The one primary flower which produces 100 per cent 

 aborted pollen bore intermediate anthers and abortion was more likely 

 due to the partial suppression of stamens, in some w^ay connected with 

 the tendency toward dieciousness, than to other causes which may result 

 in sterility. This was not included in the average percentage of aborted 

 pollen in the primary flowers for this reason. 



A comparison of the pollen condition in the flowers borne on various 

 positions shows that pollen i.,bortion is in no way related to flower position 

 and thus to dieciousness as are the various anther types and sterile pistils 

 before mentioned. 



In the hermaphroditic species F. americana nearly the same condition 

 exists with regard to the degree of perfection of pollen as in F. virginiana. 

 The result of pollen counts on 49 flowers taken from an equal number of 

 plants are shown in Table VI and they indicate that the pollen condition 

 of F. americana is normal. As it is very difficult to cross F. virginiana 

 and F. americana, it is probable that where these two species are growing 

 in close proximity they remain pure. 

 38325°— 18 2 



