96 MR. C. DARWIN ON THE DIMORPHIC CONDITION IN PRIMULA. 
the Boraginee, Prof. Gray finds a new and inexplicable case,— 
namely, some specimens with the stamens and pistil sub-exserted, 
and other specimens with both organs seated low down the tube of 
the corolla. Dr. Torrey and Prof. Gray have designated all such 
plants as “ diceciously dimorphous. ” Tn the Labiate, Mr. Bentham 
informs me that several species of Atgiphyla, and some of Mentha, 
are dimorphic like Primula. The case of Thymus is different, as I 
know from my own observations; but I will not here enlarge on 
this genus. Again, as I hear from Mr. Bentham, numerous species 
of Oxalis are similarly dimorphic. I can add the genus Linum. 
So that we already know of species (generally several in the same 
genus) having distinct dimorphic individuals, as far as structure 
is concerned, however it may prove in function, in no less than 
eight natural orders. 
With respect to Linum, I will not here enter on details, as I in- 
tend to try further experiments next summer; but I may state, 
that I observed many years ago two forms in Linum flavum, with 
both the pistils and stamens differing in length. In Linum grandi- 
Jlorum there are likewise two forms which present no difference in 
their male organs, but the pistil and stigmatic surfaces are much 
longer in the one form than in the other. "The short-styled form, 
I have good reason to believe, is highly fertile with its own pollen; 
whether it be more fertile with the pollen of the long-styled form, 
I cannot at present say. The long-styled form, on the other hand, 
is quite sterile with its own pollen: several plants grew in my 
garden, remote from the short-styled plants; their stigmas were 
coloured blue with their own pollen; but although they produced 
a vast number of flowers, they did not produce a single seed- 
capsule. It seemed a hopeless experiment; but I had so much 
confidence from my trials on Primula, that I put a little pollen 
from the short-styled plants on the stigmas (already blue with 
their own pollen) of twelve flowers on two of the long-styled 
plants. From these twelve flowers I got eight remarkably fine 
seed-capsules ; the other flowers not producing a single capsule. 
The existence of plants in full health, and capable of bearing 
seed, on which their own pollen produces no more effect than 
the pollen of a plant of a different order, or than so much in- 
organic dust, is one of the most surprising facts which I have ever 
observed. 
