Briefe. 
129 
This last pod grew very well in the beginning, even more rapidly than 
most of the other pods of the same plant; being fertilized Jan. 17. Febr. 28^'^ it 
had a length of 30 while a pod fertilized at the same time with Oncidium 
pubes had only 23 Notwithstanding all the seeds of the latter were apparent- 
ly good. In the seedless pod of Oncidium flexuosum crossed with Cyrtopodium 
the hygfoscopical hairs on the inside of the valves, so common among Orchids, 
are unusually well developed. 
How wonderful is the fact, which you observed, of the difference of growth 
in the plants produced from self-fertilized and crossed seeds and what a fine 
gradation we now already have in the results of self-fertilization, from the less 
vigorous growths of the produced seedlings, through lessened number or total 
want of good seeds, to the mutual poisonous action of pollen and Stigma. 
I have lately begun collecting our ferns and in a two weeks brought together 
about 50 Speeles, belonging to more than 30 genera. It is a curious fact that 
even now the first leaves (I do not know the proper English term for the „frons" 
of ferns) of many ferns exhibit the form of Cyclopteris, the dominant genus in 
the eldest fossil fern-flora. 
I enclose here two small pretty species, closely ressembling each other, 
and yet belonging to distinct genera; one of them, with anastomosing nerves 
(Doryopteris), is a most common species; the other, with free nerves (Pellaea), seems 
to be very rare and I have always found it in Company of Doryopteris^). The 
leaves of Pellaea are generally a little more divided, but I have often been unable 
to say to which of the two species a plant belonged without looking for the nerves. 
A Campyloneuron growing almost always in Company of a very common 
Drynaria also ressembles to this latter so closely, that sterile plants can often 
hardly be distinguished without examining their nervation. I already mentioned, 
I think, a small Oncidium from Theresopolis, growing in Company of and closely 
ressembling by its pseudobulbs and leaves to Oncidium unicorne, to which it 
has no close systematical affinity. — Many years ago I was Struck by a Papilio- 
naceous plant, which at first sight deceived by the colour of its leaves and flowers, 
I had mistaken for a common littoral Ipomoea, among which it grew. (S. 98.) 
In most of these cases of two species of different genera or families growing 
in Company and closely ressembling each other in colour or odour, or form, it 
will be very difficult, if not impossible to decide, whether this ressemblance is 
due to adaptation to the same condition of life or to mimicry. In the case of 
the Leguminosa it seems to me by far more probable that it is a mimetic 
plant 
I had thought at publishing a httle book containing misceUaneous zoological 
observations, but on communicating the plan to a friend of mine I knew that it 
would be difficult to find a publisher for such a book in Germany; so I have 
given up the idea. 
Die Antwort auf diesen Brief ist vom 3i.July und findet sich in Darwin, Life and 
letters, III, p. 70. Uebersetzung von Viktor Carus, III, S. 68. Die in dem Briefe an- 
gekündigte Zusammenstellung Müllerscher Beobachtungen über Giftwirkung eigenen* Pollens 
i) Brief an Hermann Müller vom 30. Mai 1867, S. 127. 
Alfred Möller, FritJ Müller, Werke, Briefe und Leben. 
9 
