30 BTLLETIX ]19n, U. S. DKPARTMEXT OF AGRICULTURE. 



acter.'' In a later paper. Salamaii and Lesley (19) extend this con- 

 ception. 



It is clear that there are many grades of pollen abortion in cul- 

 tivated potatoes and that even in the highest grade of pollen fertility 

 there is much abortion. There is no sharp distuiction between 

 presence and absence of good pollen. There is scant evidence that 

 ' an}^ varieties most highly potent as males will breed true for this 

 condition. But abundant evidence is found that they usually do not 

 breed true and that regression to lower grades of pollen sterilit}' mav 

 be different for reciprocal crosses. The interpretation that such 

 results (19) are due to specific hereditary factors which are dis- 

 tributed differentl)' to the spores in pistils than to the spores in 

 stamens, through a somatic segregation that precedes the regular 

 reduction divisions, is an expression of the view that there must be 

 direct hereditary bearers of pollen sterility and pollen fertility. It 

 seems to the writers that tlie presence of pollen sterility of some 

 degree in all cultivated varieties and seedlings derived from them is 

 proof that pollen sterility is really perpetually dominant. The whole 

 race of cultivated potatoes is decidedly low in maleness. The heredi- 

 tary values of the different grades and the type of inheritance involved 

 can only be determined by an extensive study of the whole group 

 of cultivated varieties and of their progenies in considerable numbers. 



Direct evidence is at present lacking as to the origin of the condition 

 of male sterility in the potato. The presence of this type of sterility 

 in certain wild species suggests possible inheritance from a wild 

 ancestor. Whether a very general one-sided sterility affecting 

 maleness {done can arise in a progeny through hybridization is an 

 unsettled point. In general, sterilit}- from iiybridity typically 

 affects botn maleness and femaleness quite alike. Variaticm in sex 

 is a widespread phenomenon among plants and animals; often it 

 gives a wide range of intersexes with females, males, and various 

 sorts of imperfect as well as perfect hermaphrodites. In some wild 

 species as well as in the cultivated potatoes there is a very general 

 loss of male potency, with little or at least relatively less loss of 

 femaleness. These conditions exist in species propagated exclusively 

 by seeds as well as in those that readily propagate by vegetative means. 



It is to be noted in this connection that the true sex stage in the 

 alternation of generations in flowering plants is reduced to a short- 

 lived, relatively simple but highl}- specialized depcntlent structure. 

 Sexual reproduction has become more and more n matter of seed 

 producing, and fruit and seed development has become decidedl)' 

 mterrelated with the vegetative growth of the plant (hat bears the 

 spores. It may well be that in tlie general evolutionary trend to 

 tnis condition the internal regulation of development and the influ- 

 ences of vegetative vigor may result in a systemic or plethoric sterility, 

 which in the case of the y">otato seems to affect iiinlcn(>ss more than 

 femaleness, and thai in time this becomes decidedly if indirectly 

 hereditary.^ 



• Since this bulletin wont to tho printer, an article by W. J. Young (Amcr. Jour, of HoUiny, v. 10, no. 6, 

 pp. 32.V.TJ4, June, I'iiZi) reports lh;»t bliistinK or nonblooinintj and i)ollon sterility in the notiito involve 

 churacteristic diiTorenecs in the dogencratioii of Kcrm cells. In the tuiislinp imd slieddini; of llowers under 

 unfavornblo weather coiuliUons there is an early degeneralion of both ovules and anther contents. But 

 in pollen sterility disinteRration of pollen (grains' occurs when they are nearly mature and do»>s not lead to 

 the sheddiuR of llowers. Vouiig also points out that varieties wliich prodiico no viable pollen may set 

 fruit anil produce seed. 



