AlUiiiat'uKj J initial and Biennial Ilahil. 305 



the distance between the plants was praclically the same 

 there were about the same number of plants that devel- 

 oped stems as there were on the margin of the sand bed, 

 in fact a little less, 53% amongst 348 plants. 



Our main result therefore is that the proportion of 

 plants wdiich developed stems in the center of the sand 

 bed is 34% as against the 53% and 60% amongst the 

 plants on the margin of this bed and in the control bed 

 respectively. Equally striking w^as the sudden change 

 in the behavior of the central plants in July. This pointed 

 to some special cause. I suspected that it was connected 

 with the growth of the roots and that these about this 

 time had penetrated the layer of sand and reached the 

 fertile earth beneath it. When I dug up the roots at the 

 conclusion of the experiment I found that these were, 

 as a matter of fact, longer than half a meter and had 

 branched freely below the level of the sand. 



In order to find out whether this was the real cause 

 of the development of the stems I made an experiment 

 in 1891 with a bed in which the layer of sand was much 

 deeper (one meter). A part of the original sand bed 

 wliich was only one-half meter deep, and a neighboring 

 bed filled with ordinary good garden soil served as con- 

 trol. This time the bed was surrounded by boards and, 

 consequently, there w^as no difference in the behavior 

 of the central and marginal plants. For this experiment 

 I used the seeds of a culture of Oenothera ruhnnerris 

 which had been cultivated as an annual for two genera- 

 tions (seeds of 1890 of the pedigree of Vol. I. p. 273). 

 The sowing took place in May 1891. At the end of July 

 I recorded the plants on the three beds, each of which 

 was 3 square meters in extent. 



