10 BULLETIN 195 ; U. S. DEPARTMENT OF AGRICULTURE. 
East estimates that about 60 per cent of the potato varieties 
belong to the first class and says that of the remaining 40 per cent 
only about 60 per cent have their blossoms persistent for more than 
a day. Our observations do not substantiate these statements, 
but this does not necessarily refute them if we regard East's data 
as applying merely to the particular locality in which his studies 
were made. The percentage of varieties belonging to any given 
class varies with the region and is very largely dependent upon the 
climatic conditions under which the plants are grown. In the 
opinion of the writer, most varieties will produce some blossoms 
when grown under optimum conditions for the normal development 
of the plant, particularly if these conditions prevail during the 
stage at which flower buds are formed. In any considerable varietal 
collection it is inevitable that many varieties should find the condi- 
tions unsuitable for their maximum development. 
In studying the microscopic appearance of the pollen of different 
varieties, East 1 found that there was a great variation in the size 
and apparent vigor of the pollen grains. In describing them, he 
says: 
Normal healthy pollen is round and about 36 p. in diameter, while unhealthy pollen 
is scarcely ever over 20 ji in diameter and is shriveled and irregular. 
It was further observed that among the normal healthy pollen 
were some grains with from one to five slight protuberances which 
contained nuclei. It was also noted that the viability of the pollen 
was greater when these multinucleate pollen grains were present, 
and the suggestion is made that microscopic examination to deter- 
mine the presence of such nuclei affords an easy and satisfactory 
method of determining whether the pollen of a given variety can be 
successfully employed. 
The observations of East in regard to crosses have been fully 
corroborated by the writer, and further reference to them will be 
made in a later portion of this bulletin. The present almost total 
absence of seed balls on most of our commercial varieties, in the 
light of our present knowledge, is explainable on the basis that com- 
paratively few of them develop viable pollen. 
In a rather recent publication Salaman 2 announces that male 
sterility in the potato is a dominant Mendelian character. The 
data presented by Salaman would seem to amply justify this asser- 
tion. This evidence is in close harmony with what is actually 
encountered in the field, as it fully accounts for the striking scarcity 
of varieties which can be successfully employed as pollen parents. 
i East, E.M. Op. cit.,p. 40. 
2 Salaman, E.. N. Male sterility in potatoes a dominant Mendelian character . . . In Jour. Linn. Soc. 
[London], Bot,, v. 39, no. 272, p. 301-312, 1910. 
