IN THE SPECIES OF PRIMULA. 95 
not, as has sometimes been maintained, mere dissemination. The 
whole subject is as yet hidden in darkness. 
I will now only add that cases of dimorphism, like that of Pri- 
mula, seem to be far from rare in the vegetable kingdom, though 
they have been little attended to. A large and important class of 
analogous facts will probably soon be discovered. Professor Asa 
Gray * informs me, that he and Dr. Torrey have described several 
Rubiaceous genera, in which some plants have exserted stamens, 
and others exserted pistils. “ Mitchella offers an interesting in- 
stance of this structure from its relationship, through Nertera, to 
Coprosma, one of the few dicecious genera of Rubiacee, and in 
which the stamens are elongated in the male flowers and the styles 
in the females." The long-styled hermaphrodite flowers of Mit- 
chella would probably be found more productive of seed than the 
short-styled ; in the same way, but in a reversed manner, as in 
Primula, the short-styled flowers are more productive than the 
long-styled ; from which fact I inferred that, if Primula were to 
become dicecious, the females would have short pistils and the 
males short stamens, these being the corresponding organs neces- 
sary for a heteromorphic union with full fertility. In the diccious 
Coprosma, on the other hand, the females have long pistils, and 
the males have long stamens. These facts probably show us 
the stages by which a diccious condition has been acquired by 
many plants. 
Prof. A. Gray also informs me that another Rubiaceous genus 
(Knoxia) in India has been described by Dr. Wight, with a 
similar structure; and this, I am told, is the case with Cinchona. 
Several species of North American Plantago are dimorphic, as is 
Rhamnus lanceolatus, as far as its female organs are concerned. 
In the Boraginee, Dr. Torrey has observed a strongly marked in- 
stance in Amsinckia spectabilis: in some dried flowers sent me by 
Prof. Gray, I find that the pistil in the one form is more than 
twice as long as in the other, with a corresponding difference in 
the length of the stamens; in the short-styled flowers the grains 
of pollen, as in Primula, apparently are larger, in the proportion 
of nine to seven, than in the long-styled flowers, which have the 
short stamens; but the difference can hardly be determined with 
safety in dried flowers. In Mertensia alpina, another member of 
* See also Prof. Asa Gray’s ‘Manual of the Botany of the N. United States, 
1856, p. 171. For Plantago, see p. 269. 
