MUTATIONS, VARIATIONS, AND RELATIONSHIPS OF THE OENOTHERAS. 21 



It will be noted that there has been a slight fall in mean heights, but the 

 most noteworthy thing in this comparison is the great increase in the varia- 

 bility. A study of fig. I shows the difference in variabilit)' quite clearly in 

 the greater amplitude and less height of the 1905 curve. The interesting 

 fact becomes apparent that although the mean value of stem-heights in 1905 

 was less than that for 1904, some of the 1905 plants were taller than the tallest 

 in 1904. The explanation of these facts is very simple. The garden at the 

 Station for Experimental Evolution has been under cultivation so short a 



66-70 71-75 76-80 81-85 86-90 91-95 96-100 101-105 106-110 



Fig. 1. — Variation in height of stem of Oenothera lamarckiana. Broken curve represents 

 the condition at the Xew York Botanical Garden in 1904, continuous curve that at the 

 Station for Experimental Evolution in 1905. 



time that it still lacks much of that homogeneity that is desirable for work of 

 this nature. One corner of this plot of Oenothera lamarckiana dipped into a 

 slight depression which received the drainage from the roof of the laboratory 

 and was therefore kept, during a portion of the growing season, too wet for 

 the best development of the plants. A few specimens on this corner did not 

 make flower-stems at all, and it was to be expected that those nearest this 

 corner of the plot would be somewhat influenced by the same unfavorable 

 conditions and made to produce flower-stems of a shghtly less altitude. 



The stature of Oenothera rubrinervis. — In 1904 a comparison was made 

 between the statures of Oenothera nanella and 0. lamarckiana, and it was a 



