FLORAL BIOLOGY. 211 



observations made upon the floras of different regions enable 

 comparisons to be instituted, and it is found that a species 

 may be gynodicecious in one country and not in another ; 

 and that, further, in any one place, the proportion of 

 hermaphrodite to female flowers may vary enormously, 

 both from one year to the next, and within the limits of 

 a single year. A plant which is at one time hermaphrodite 

 may even change to female in a short time, or vice versa. 

 The phenomenon may under certain circumstances {e.g., 

 in early spring or in late autumn) appear in almost any 

 plant. Again, nearly all species which are usually gyno- 

 dicecious exhibit gynomoncecism also, female flowers occur- 

 ring in greater or less number upon the hermaphrodite 

 plants. Gynomoncecism also is a phenomenon varying 

 in degree and from place to place. 



So variable and inconstant is gynodicecism that it can 

 scarcely be regarded as hereditary, though it usually appears 

 in certain Labiatai and one or two other plants. It has not 

 been shown to be in any way advantageous to the species 

 possessing it, but it has been taken for granted that it is 

 an adaptation to cross-fertilisation. After what has been 

 said above it would seem better to remove it altogether, at 

 present, from the realm of adaptation, and study it more 

 thoroughly on its own account. 



Similar considerations apply to the phenomena of andro- 

 moncecism, etc. Here the male flowers are usually at the 

 distal end of the inflorescence or on small lateral twigs, and 

 their production almost certainly depends on lack of nourish- 

 ment. [Somewhat similar phenomena are seen in monoe- 

 cious plants, so that there may be a closer connection 

 between these phenomena than is usually supposed to 

 be the case.] 



A consideration of all that has been said so far leads 

 naturally enough to the conclusion that one of the great 

 desiderata just now is a study of the details of the nutrition 

 of plants, more especially what we may term the local 

 nutrition. We want to know the causes which determine 

 the amount of food that goes to the various parts — the 

 vegetative organs (including such as are detached for 



