HETEROGAMY. 193 
Change from the monecious to the diwcious condition—'lhis 
is of less frequent occurence than might have been 
anticipated. In the ‘Gardeners’ Chronicle,’ 1847, 
pp. 541 and 558, several instances are noted of walnut 
trees bearing female flowers to the exclusion of males. 
The mulberry tree has also been noticed to produce 
female blossoms only, while in other plants male 
flowers only are developed. 
It seems probable that the age of the plant may 
have something to do with this production of flowers 
of one sex to the exclusion of the other. 
Change from the diccious to the monecious condition.—Andro- 
gynism—T'his is of far more common occurrence than 
the preceding. 

Fie. 101—Monecious inflorescence of Hop. 
In the hop (Humulus LInpulus), when moncecious, 
the female catkins are usually borne on the ends of 
the branches as shown in the cut (fig. 101), and a similar 
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