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^' DIMORPHISM IN THE GENITALIA OF FLOWERS. 
By PROFESSOR Asa GRAY, 
Two principal:kinds of dimorphism in the genitalia of flowers have 
been noticed ina great number of instances, and put on record in 
various works ; but the instances have not been collected and systema- 
tized, nor had the import of the most curious case been made out until 
elucidated by Mr. Darwin. There is, first, the dimorphism which Mr, 
Darwin has illustrated in his paper ** On the two forms, or Dimorphie 
Condition, ‘in the species’ of Primula.” This was long ago named 
dicecio-dimorphism (see Flora of N. America, ii. p. 38, ete.), a name 
‘which pretty well expresses the thing as now understood ; for these 
‘blossoms, although hermaphrodite structurally, are functionally as if 
diccious or nearly so, the end subserved: being fertilization of the 
vules of one flower by the pollen of another flower on another indi- 
vidual, 
The dicecio-dimorphous species of Pluntago had seemed to coufuse 
‘this case with the next; that is, the short-stamened flowers appeared 
to be fertilized in the closed flower, and the long-stamened and gene- 
rally sterile plants therefore to be generally useless. This could hardly 
be; and a recent observation on a single specimen (likely to be con- 
firmed in others) shows the top of the style projecting from the tip of 
the closed corolla: This refers the case to the same category with 
Houstonia, Primula, ete., to which P. pusilla and P. heterophylla, 
having the éorollas of the short-stamened form open in anthesis and 
the stigma projecting, evidently belong. It is to be noted that dimor- 
phism, both of this and of the following sort, is apt to be variable, 
“either in mode or in degree, in different species of the same genus, and 
also that it seldom occurs in all the species of a genus, some of them 
being unaffected, while others in some genera are nearly polyga- 
‘mous or diceious, —which is all very favourable to the conclusions that 
Mr. Darwin wishes to draw. | 
"he second case, which equally belongs to structurally hermaphrodite 
flowers, is practically the reverse of the first. It is the case in which, 
besides the normal flowers of the species, which for the most part are 
rarely or sparingly fertile, other flowers are produced which never open, 
their development being as it were arrested in the bud, but remm are 
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