26 BULLETIN 1195, U. S. DEPARTMENT OF AGRICULTURE. 
The 29 plants of Solanum jamesii grown from tubers and listed in 
Table 6 represented 23 known different clons, and these were selfed in a 
total of 169 flowers. Only five seed balls were obtained, one from 
each of five plants. There is some pollen impotence in this species, 
but in most cases at least half of the pollen is vigorously viable. It 
appears that this stock is either only feebly self-compatible or that 
abscission was very decided under the particular conditions of 
growth. Of 12 combinations in crosses only two succeeded, which 
suggests that cross-incompatibility is in evidence. 
The plants of Solanum maglia which have thus far been grown at 
Presque Isle have all been so highly pollen sterile that they could not 
be expected to function as pollen parents irrespective of any real 
incompatibilities that might be present. 
The compatibility between the various wild species and between 
these and the cultivated varieties awaits the completion of investiga- 
tions now under way. 
RESULTS OF THE STERILITY SURVEY. 
The survey has clearly shown that two types of sterility exist in 
cultivated potatoes: (1) Sterility from nonbtooming and abscission 
and (2) pollen sterility or one-sided impotence, giving loss of maleness. 
In wild species as grown at Presque Isle, early abscission of flowers 
is rarely seen, but in certain species pollen sterility is marked, and 
there are also evidences of physiological incompatibilities. In the 
hybrids between the two species Solarium fendleri and S. chacoense 
there is very decided impotence of both pistils and stamens. 
The sterility from nonblooming to a large degree can be overcome 
for seed-breeding work by growing varieties under cool-season condi- 
tions such as prevail at Presque Isle. There are without doubt some 
variations in the potency of pollen in fully developed flowers of a 
single variety, possibly even for the various flowers of a single cluster, 
and it may be possible that special conditions may shift the pollen 
of a variety even from class 1 to class 3 or the reverse, but there has 
been no indication of this in studies made thus far. 
Success in obtaining seed depends decidedly on using as male 
parents varieties which yield the most viable pollen. But even in 
the best pollen producers among the cultivated potatoes there is 
much abortion of pollen. As a group these varieties are decidedly 
low in maleness but relatively high in femaleness. 
Other studies of the condition of potato pollen in its relation to 
sterility include those of Turner, Dorsey and Breeze, respectively. 
In studies of the pollen of 11 leading commercial varieties grown at 
Presque Isle, in 1918, Turner 2 found a very high percentage of the 
grains to be imperfect. In the 61 seedlings studied he reported 
a wide range of variability in the quality of the pollen, with germina- 
tion ranging from to 75 per cent. From tests of pollen from plants 
grown without fertilizer and with different ratios of fertilizer ingredi- 
ents he concludes that nutrition has a marked effect on the via- 
bility of pollen. Dorsey (3) found that a large percentage of the 
pollen of several of the best-known varieties grown in Minnesota 
was imperfect. He concludes that the development of the pollen 
9 From unpublished manuscript by Thomas W. Turner. 
