FLOWERS AND POLLINATION 



But there are myriads of flowers which are not 

 perfect — which are unisexual or single sexed. Some 

 scientists indeed are of the opinion that there is a 

 tendency in all forms of plant Ufe toward flowers of 

 the unisexual form — that it is the step forward in the 

 evolution of vegetation — but that is too big a subject 

 to consider here, besides being wide of the question. 



The important thing for us is to know that these 

 two kinds of flowers are borne in two distinct ways on 

 the plant. Sometimes the two sexes are upon the same 

 plant, as in the oak; at other times they are upon sepa- 

 rate plants. The willow is an instance of this. When 

 both are found upon one plant it is said of that species 

 that it is monoecious or ''of one household;" when they 

 are upon separate plants the species is dioecious or 

 "of separate households." 



There is a still further variation, some species 

 producing the two kinds of flowers — those that are per- 

 fect or bisexual and also those that ar^ unisexual — and 

 both kinds — staminate and pistillate — of the latter. 

 These plants are called polygamous. Common bitter- 

 sweet of woods and thickets is an example, also the 

 horsechestnut, maple, sumach, honey locust — and 

 many others. 



The importance to the gardener of this variation 

 in flowers lies in its bearing so directly upon the pro- 

 duction of seed, otherwise fruit. It is of course impos- 

 sible for a solitary dioecious plant to produce fruit, even 

 though it is of the fruiting or pistillate form. Here is a 

 staminate sassafras tree, outside the window, yellow with 



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