240 



University of California PuMications in Botany [Vol. 



Table I details the results of germination tests, some of which are 

 expressed more briefly in tables II, Ila, and 116. The data submitted 

 furnish a confirmation of the results previously reported, which demon- 

 strated that tobacco seed five years old and older will give a relatively 

 high percentage of germination under controlled conditions. As to 

 whether deterioration in viability is a gradual process or has a sharp 

 end-point after which viability is greatly reduced we can, again, make 

 no generally applicable answer. The combined evidence furnished by 

 the previous experiments and those above submitted seems to make 

 it clear that for certain species and varieties the end-point is abrupt, 

 while for others deterioration as to viability is a gradual process. 

 This distinction can be made even within a species, since the various 

 N. Tahacum varieties differ from one another as to the amount of seed 

 which becomes functionless in each succeeding year. In this con- 

 nection attention should be called both to the uniformity and to the 

 lack of uniformity in the rates of germination of the seed of various 

 varieties within a given species. Take, first, the six varieties of N. 

 Tahacum, the seed of which is dealt with in this and in the preceding 

 report. Table II& combines results given in Table 3 of the preceding 

 report (Goodspeed, 1913, p. 210) with certain of those included in 

 Table I and lays emphasis upon the number of days during which a 

 significant amount of germination took place as well as the day, dur- 

 ing the extent of the germination test, upon which the greatest amount 

 of germination was noted. As Table II& shows, there is an extraor- 

 dinary uniformity as to the day upon which the greatest amount of 

 germination took place. There is, in a number of cases, a character- 



