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 

 chmatic 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 poUen of different 

 varieties, East ^ 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 /j in diameter, while unhealthy pollen 

 is scarcely ever over 20 jx 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 viabihty 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 fuUy 

 corroborated by the writer, and further reference to them will be 

 made in a later portion of this bulletiu. 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 poUen. 



In a rather recent pubhcation Salaman ^ announces that male 

 sterihty in the potato is a dominant Mendehan 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 poUen parents. 



lEast, E.M. Op. cit., p. 40. 



2 Salaman, R. N. Male sterility in potatoes a dominant Meudelian character . . . In Jour. Linn. Soc. 

 [London], Bot., v. 39, no. 272, p. 301-312, 1910. 



