POTATO BKEEDIIs'G AND SELECTION. 11 



RESULTS OF EXPERIMENTAL CROSSING. 



Although many crosses were made by the wiiter prior to 1909, the 

 results secured -were of such a meager nature as to be unworthy of 

 mention. In 1909, however, so many successful crosses were made 

 as to cause the writer to inquire the reason thereof. This inquiry 

 he has been unable to answer more satisfactorily than to suggest that 

 it may have been due to more favorable growing conditions at the 

 time the plants were developing buds and flowers, thus furnishing 

 the right conditions for the development of viable pollen. 



One of the main objects of the 1909 experiments was to secure as 

 many crosses as possible between the disease-resistant German varie- 

 ties and those American varieties which would cross with them. 

 The anxiety to succeed was perhaps responsible for the use of a few 

 undesirable pollen parents, which always afforded an abundance of 

 viable pollen and could therefore be depended upon to effect a cross 

 when all other sources failed. The abundant results secured served 

 to convince the writer of two facts which had previously been rather 

 puzzling: (1) It demonstrated conclusively that the ovaries and 

 pistils of many of the varieties in the collection were normally devel- 

 oped and that lack of success was not due to this cause, and (2) it 

 emphasized the necessity of paying greater attention to all varieties 

 which produce viable pollen, as well as to those which produce it 

 sparingly or not at all. A further observation was also made with 

 respect to the secretion of stigmatic fluid by the glands of the stigma. 

 Practically every writer who has had occasion to describe the potato 

 flower in connection with the subject of plant breeding has told his 

 readers that the stigma is in a receptive condition when it is covered 

 with a fluid secretion. This condition of the stigma has rarely been 

 observed and then only when the pistil has passed beyond the stage 

 of successful fertilization. It is doubtful whether the secretion of a 

 stigmatic fluid is a normal function of the potato blossom at the 

 present time. 



Tlic accompanying record of the 1909 crosses, which is presented as 

 Table I, gives the parentage, number of flowers crossed, number of 

 seed balls developed, percentage of success, and the number of seed- 

 lings that produced tubers. 



A study of Table I discloses some rather interesting data, partic- 

 ularly with respect U) the behavior of seed-bearing plants when pol- 

 linated with (Hfferent vari<^tifis. In the first cross recorded, G(»,heimrat 

 Thf'il / K^'ejKT, six flowers Were pollinated and Ave seed balls wore 

 developed, from which .502 tuber-bearing plants were produced. 

 Thf Hurne vari<'ty when niati'd with XX Early developed only one seed 

 ball from 1 1 p<)llinat/<'(l flowers, and this did not ])ro(luc(^ a single 

 tuber-bearing plant. When crossed with Solanum maglia, a wild 

 Soiith Airuirifun s])(!ci(!S, it failed to set fruit, and tlie same ncigative 



