PARTIAL DICLINISM. 229 



clearly is a question of the distribution o£ mitrition ; the 

 loieer, being the later ones to expand, are the weaker.* 

 Muller mentions Horse-chestnuts as being also andro- 

 monoecions ; and what is exceptional is that the hermaphro- 

 dite flowers are protogynous. This, however, may be due 

 to the early period of flowering, like species of Fnmus and 

 CratcBgus. 



The reader will now perceive that there may be several 

 causes at work to produce these kinds of " partial diclinism ; " 

 and tliat what is required is to ascertain, if possible, by 

 observation and experiment, which is the one peculiar to 

 each species. Secondly, when any one or more causes has 

 been suflBciently persistent, the results become hereditary ; 

 so that certain species, genera, and orders become more or 

 less chai-acterized by these peculiar features. 



* Compare the observations on Adoxa, p. 188. 



22 



