30 BULLETIN 1195, U. S. DEPARTMENT OF AGRICULTURE. 
acter." In a later paper, Salaman 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 distinction between 
presence and absence of good pollen. There is scant evidence that 
any 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 sterility may 
be different for reciprocal crosses. The interpretation that such 
results (19) are due to specific hereditary factors which are dis- 
tributed differently 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 the 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 alone can arise in a progen} r through hybridization is an 
unsettled point. In general, sterility from hybridity typically 
affects both maleness and femaleness quite alike. Variation 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 highly specialized dependent structure. 
Sexual reproduction has become more and more a matter of seed 
producing, and fruit and seed development has become decidedly 
interrelated with the vegetative growth of the plant that bears the 
spores. It may well be that in the general evolutionary trend to 
this 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 potato seems to affect maleness more than 
femaleness, and that in time this becomes decidedly if indirectly 
hereditary. 3 
s Since this bulletin went to the printer, an article by W. J. Young (Amer. Jour, of Botany, v. 10, no. 6, 
pp. 325-334, June, 1923) reports that blasting or nonblooining and pollen sterility in the potato involve 
characteristic differences in the degeneration of germ cells. In the blasting and shedding of flowers under 
unfavorable weather conditions there is an early degeneration of both ovules and anther contents. But 
in pollen sterility disintegration of pollen grains occurs when they are nearly mature and does not lead to 
the shedding of flowers. Young also points out that varieties which produce no viable pollen may set 
fruit and produce seed. 
