THE CATKINS OF THE WILLOW 



to that question is, most probably, that at the time 

 the tendency to produce nectar originated, the 

 sexes of these flowers did not grow on separate 

 trees. I have already shown in the case of the 

 sycamore how flowers of one sex are evolved from 

 the bisexual form, and how unisexual and bisexual 

 forms may be found together on the same tree ; 

 and likewise in the case of the ash flowers. 



Therefore, should the tendency to develop 

 nectar occur while the unisexual catkins were grow- 

 ing together on the same tree, the flowers of each 

 would naturall}^ develop similar characteristics, and 

 so both produce nectar. However, any tendency 

 in a tree to produce an abnormal number of female 

 catkins would confer benefits upon its species, as 

 many of its flowers would then have to receive 

 pollen from another tree ; which would result in 

 a more effectual cross-fertilisation than from pollen 

 from flowers on the same tree. And an excess of 

 male catkins would largely prevent their pollen 

 from being used on the females of that same tree. 

 Therefore, encouraged by the continual visits of 

 bees seeking pollen and nectar (which insured 

 cross-pollination), the habit of developing their 

 sexes on distinct trees was strengthened. Thus 

 to-day we find them completely isolated ; so much 

 so that great confusion has prevailed amongst 

 botanists in enumerating the species and matching 

 their sexes, especially as many species flower 

 before the leaves appear. 



Such are some of the remarkable ups and 

 downs experienced by the ^^palm" willow in 



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