PARTIAL DICLINISM. 229 



clearly is a question of the distributiou of nutrition ; the 

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

 Miiller mentions Horse-chestnuts as being also andro- 

 raonoecious ; 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 Prunus and 

 Gratcegus. 



The reader Avill now perceive that there may be several 

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

 and that 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 sufficiently persistent, the results become hereditary ; 

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

 less characterized by these peculiar features. 



* Compare the observations on Adoxa, p. 188. 



