( 399 ) 
characters is increased when nutrition and selection act in opposite 
directions, i.e. when, as in his experiments, strong nutrition goes 
together with negative selection. 
Also the experiments by Rermönr *) on the variability of the number 
of stamens of Stellaria media show that with good nutrition the 
median of this character possesses a higher value than with bad 
nutrition. Besides Rreiönr finds that the index of variability, which 
is a measure for the variability, becomes smaller under unfavourable 
nutritive conditions. 
Weissr *) investigated the influence of nutrition on various charac- 
ters of Helianthus annuus and found that the arithmetical mean for 
all the characters studied is smaller with plants cultivated on a sandy 
soil than with well-fed plants. His numbers, (for each culture about 
forty) are too small, however, to allow us to calculate the constants 
for median and variability from them and to draw conclusions from 
these. 
Mac Lrop*) made experiments in order to determine the influence 
of nutrition on the number of ray- and disk-flowers of Centaurea 
Cyanus and found that this number is the smaller the more the 
nutritive conditions are unfavourable. Besides he investigated the 
influence of good and bad nutrition on the number of stigmatic-rays 
of Papaver Rhoeas coccineum aureum. He arrived at the result that 
with the badly-fed plants the median is considerably smaller, but 
that the variability of the character is increased by the bad nutrition. 
From this short summary it will appear that in very few cases 
only the quantitative change, caused in the median by varying nutri- 
tion, has been determined. It is desirable to extend the number of 
observations on this point, but it is especially important to learn the 
influence of nutrition on the variability for several characters and 
plants. Two questions here arise, in the first place whether this 
influence is different for different parts of the same plant, in agree- 
ment with VerscHarrent’s *) result that the variability itself of diffe- 
1) Frrepricn Reréut, Die Variation im Andröceum der Stellaria media Cyr. Bot. 
Zeit. 1903, p. 159. 
2) AntHur Wersse, Die Zahl der Randbliithen an Compositenköpfchen in ihrer 
Beziehung zur Blattstellung und Ernährung. Jahrb. f. wiss. Bot. Bd. 30, 1897, p. 453. 
5) J. Mac Leop, On the variability of the disk- and ray-flowers in the cornflower 
(Centaurea Cyanus). Hand. v. h. 3de Vlaamsch Nat. en Geneesk. Congres, Sept. 
1899, p. 61 (in Dutch) and On the variability of the number of stigmatic-rays in 
Papaver. Hand. v. h. 4de Vlaamsch Nat. en Geneesk, Congres, Sept. 1900, p. 11 
(in Dutch). 
1) Ep. Verscuarrett, Ueber graduelle Variabilität von pflanzlichen Wigenschaften. 
Ber. d. d. bot. Gesellsch. Bd. XII, 1894, p. 350. 
