THE NUMBER OF STAMENS AND CARPELS. 217 
vespertina, Sibth., Rumex Acetosella, Linn., &c. Meehan’ observes 
that severe competition causes in Ambrosia artemisifolia, Linn.,the 
proportion of male plants to be increased. Such observations, 
parallelled by those of Prantl, Borodin and Magnus on starved 
prothalli, and of Klein on Volvox, show that in many cases the 
sex in dicecious plants is influenced by external conditions. 
Again, when, as abnormalities, female or hermaphrodite flowers 
appear on male or female plants, these generally occupy definite 
positions, showing that some influence is at work. Thus in 
Salices they are usually confined to the upper or the lower ex- 
tremity of the catkin ; and in the Hazel (Corylus Avellana, Linn.), 
when hermaphrodite flowers appear on the female catkin, or 
female flowers on the male catkin, they are at the base ^. Many 
similar cases might be given, showing that in abnormal cases of 
monecism in diccious plants, as a rule, the abnormal flowers 
occupy a definite position, and are not scattered irregularly any- 
where on the plants. In fact, the appearance of such a plant as 
Typha or Arum, where the male flowers are always fixed in 
position with regard to the female, is repeated in the abnormal 
cases quoted, showing that probably the position is due to definite 
causes, and not to spasmodic variation, such as Meehan terms 
“variety for mere variety's sake ” 1, 
Now passing from this to gynodiocism and gynomonecism, 
we have evidence that active influences exist which, if not 
causing, determine in some degree the extent of them. Willis * 
has suggested that nutrition is à determining factor in the gyno- 
dicecism of Qriganum vulgare, Linn. Warming accounts for the 
gynodiecism of the Caryophyllacew as due to the same cause. 
Ludwig explains it in Erodium '' as caused by unfavourable con- 
ditions, and as due to deficient nourishment, which in Cerastium 
9 * Changes of Flowers normally of one Sex to the other." Proc. Acad. Nat. 
Sci. Philadelphia, 1880, p. 353. . 
10 For the literature relating to this, cf. Penzig, ' Pflanzen-teratologie, 
Genoa, 1892-94. _ . 
1 “Contributions to the Life-Histories of Plants. No. IL” Proc. Acad, 
Nat. Sci. Philadelphia, 1888, p. 282. 
12 “On Gynodicecism in the Labiate " (2nd paper). Proc. Camb. Phil. Soc. 
viii. p. 17 (1892). 7 
13 « Om Caryophyllaceernes Blomster.” Festskrift Bot. Foren. p. 194 (1890) ; 
fide Just’s Jahresbericht, 1890, p. 530. u 
5 = Die Gynodioecie v. Digitalis ambigua, Murr., u. D. purpurea, L." Kosmos, 
1886, xvi. p. 107. 
