132 Mr Willis, On Gynodioecism, with a note upon [Nov. 27, 



[In the first week, 1891, only 8 plants were out, in 1892 only 7, 

 in 1893, 24.] 



It is thus evident that on the whole the female plants flower 

 a little sooner than the hermaphrodite, but the proportion, after 

 the first week, does not fall much, and has a tendency to rise 

 again later in the season. Schulz\ on the other hand, states 

 that the proportion of female to hermaphrodite plants is not 

 dependent on the season. Hence the support given to the 

 hypothesis of Hildebrand and Ludwig by these observations is, 

 if any, very slight. The author's (not yet published) observations 

 on dichogamy in Thymus serpyllum show that, though it is fully 

 dichogamous late in its flowering season (i.e. the male period 

 is over when the female begins), it is not so at first, there being 

 a considerable overlap, during which the flower is hermaphrodite, 

 and may fertilise itself This phenomenon, if general, would also 

 be an argument against the hypothesis under consideration. 



Darwin^ looks on the greater fertility of the female form as 

 the great factor in producing gynodioecism, but leaves it as un- 

 decided whether this was the first cause or whether the stamens 

 began to abort and so raised the fertility of those flowers. Schulz 

 denies the greater fertility of the female, and it should be ob- 

 served that in any case, a Labiate flower can only give four seeds, 

 which it does when it is properly pollinated, whether hermaphro- 

 dite or female. 



Taking together all the facts, it would seem that the proxi- 

 mate cause of one flower being female, another hermaphrodite, 

 is some difference in nutrition; in the case of gynodicecism, 

 between two plants, in the case of gynomonoecism between 

 flowers on the same plant. The phenomena vary largely with 

 the nature of the soil and climate, with the season of the year, 

 and other conditions. Females are apparently more common in 

 very wet situations, though occasionally the reverse is the case. 



Gynodioecism and gynomonoecism are almost invariably asso- 

 ciated with pronounced dichogamy. It seems probable therefore 

 that in dichogamous plants, the various causes mentioned above 

 may produce a considerable degree of gynomonoecism, or even 

 gynodioecism. This may prove advantageous and become per- 

 petuated by natural selection, as seems to have occurred in the 

 Labiatse and other orders. 



Many other phenomena are apparently due to similar causes 

 acting upon the plant. These may be briefly considered. 



Androdioecism, which is very rare, is almost certainly due ^ 

 to lack of nourishment of the male plant, and so too, andromo- 

 noecism to some flowers receiving a small supply. 



1 Loc. eit. ^ hoc. cit. p. 304. 



2 Miiller, "Alpenblumen," p. 41. (Veratinim.) 



