THE FLOWER 21 



are heterosporous. So far as there is any advantage in this 

 habit, however, it is practically lost if stamens and carpels are 

 present in the same flower or upon the same plant. Morpho- 

 logically the gametophytes are unisexual, but in fact they are 

 dependent upon the same individual. Any physiological advan- 

 tage, therefore, that comes from the crossing of individuals 

 must be secured by pollination or by the separation of stamens 

 and carpels upon different individuals. It is unfortunate that 

 the term " dioecious " has two distinct morphological applica- 

 tions, referring to the sexual differentiation of individuals 

 among the lower plants, and to the sporangial differentiation 

 of individuals among seed-bearing plants; but from the phys- 

 iological standpoint the distinction probably does not exist. As 

 a consequence, the dioecious habit in effect is secured in certain 

 seed-plants by the development of monosporangiate individuals, 

 and it is perhaps significant that this habit not only prevails 

 among the more primitive seed-bearing plants, but is associated 

 in the main with wind-pollination. Among the higher Angio- 

 sperms the effect of the dioecious habit is secured for bisporan- 

 giate plants by means of insect-pollination. It follows from 

 this point of view that neither the monosporangiate nor the 

 bisporangiate habit can be regarded as in itself the more primi- 

 tive. The former habit prevails among the more primitive 

 families because they are necessarily anemophilous ; while the. 

 latter prevails among the higher families because insect polli- 

 nation does not necessitate the monosporangiate habit. It 

 should be noted that Goebel (Organographie) regards the 

 bisporangiate condition as primitive, the monosporangiate 

 being derived from it by reduction. This can be demonstrated 

 in certain cases, but the monosporangiate condition is probably 

 the primitive one in many of the more primitive angiospermous 

 families. In any event, the monosporangiate and bisporan- 

 giate habits are not always settled ones. For example, in the 

 monosporangiate Amarantus retroflexus there are occasional 

 bisporangiate flowers; while in monosporangiate and dioecious 

 willows both catkins may appear on the same individuals, and 

 the catkins themselves may be mixed (staminate, pistillate, and 

 bisporangiate). It follows also that there may be monosporan- 

 giate members in all great groups (as Ranunculaceae), or even 

 in bisporangiate genera (as Rumex and Lychnis), for this habit 



