SEED WEIGHT AND GERMINATION 



269 



required for germination, and in this way probably reduce the 

 correlations and decrease the trustworthiness of the determina- 

 tions. 



Turning from the difficulties presented by the physical factors 

 to those inherent in the organisms, we note that it is not easy to 

 obtain a quantitative measure of the time required for germina- 

 tion — for there is no clearly marked stage at which geraiination 

 may be said to begin or end. The selection of a period of some 

 particular physiological significance to the plant as it grows in 

 nature seemed for the selective elimination phase of the work 

 desirable. The moment of pushing through the soil cannot be 

 used because the exact time (in individual cases) is so much 

 dependent upon the character of the substratum. Sometimes a 

 considerable tent of sand will be raised and the seedling remain 

 covered for a few hours longer; in other cases, from a slightly 

 different texture or moisture content, the seedling breaks through 

 earlier. The stage selected was that of the opening out fiat of 

 the primordial leaves. It is then that the full beginning of 

 photosynthesis is possible. To be sure, the time is influenced 

 by various circumstances, e.g., light and moisture, but it is, 

 because of its physiological significance in life in the open, a 

 logical stage, and empiricalh- it proves sufficient for first approxi- 

 mations. 



All the seedlings entered in the tables from which correlations 

 are deduced were nomial.^ 



The time required for germination was recorded in units of 

 three-hour range. The centers of these classes were taken for 

 purposes of calculation at 1, 4, 7 and 10 a.m. and 1, 4, 7 and 10 

 P.M. Thus the seedlings recorded as having germinated {i.e., 

 having opened out their primordial leaves) at 1 a.m., include all 

 those germinating between 11:30 p.m. and 2:30 a.m. of the same 

 night; those centered at 7 p.m. include all which opened their 

 leaves between 5:30 and 8:30 p.m. 



This method of measuring the time required for germination 



' These form Class A of the earlier paper, which the reader may consult for 

 details. It is impossible to draw a sharp line between normality and abnormality, 

 and personal equation probably plays some, but not a large, part. 



