x PREFATORY NOTICE. 
knows whether this difference has any functional signification, and 
this is a point which ought to be determined. Again, there are 
other plants, for instance, the common Rhododendron, in which the 
shorter stamens are more or less rudimentary, and it has been 
asserted that seedlings raised from pollen taken from the short and 
from the full-sized stamens differ in appearance; and it would be 
of importance to know whether they differ in their fertility or 
power of yielding seeds. It would also be interesting to learn 
whether in the plants, already alluded to, which produce two 
forms, one adapted for self-fertilisation and the other for cross- 
fertilisation, the reproductive organs have become in any degree 
differentiated, so that their action would not be perfect if the two 
forms were reciprocally crossed. Would a flower adapted for 
self-fertilisation yield a full complement of seed if fertilised by 
pollen from one adapted for cross-fertilisation ; and vice-versd with 
the other form ? 
But it would be superfluous to make any further suggestions, 
These will occur in abundance to any young and ardent observer 
who will study Miiller’s work and then observe for himself, 
giving full play to his imagination, but rigidly checking it by 
testing each notion experimentally. If he will act in this manner, 
he will, if I may judge by my own experience, receive so much 
pleasure from his work, that he will ever afterwards feel grateful 
to the author and translator of the Befruchtung der Blumen. 
CHARLES DARWIN. 
Down, February 6, 1882. 
