OF CERTAIN SPECIES OF ONCIDIUM. 163 
brief preliminary abstract. The species experimented upon were 
the Oncidium sphacelatum, O. altissimum, O. divaricatum var. cu- 
preum, O. graminifolium, and O. ornithorhynchum. 
First, I impregnated six flowers of the O. sphacelatum with 
pollinia of the O. divaricatum var. cupreum, from which I obtained 
four fine plump capsules. These being in an immature state, 
when I made my communication to the Botanic Society of 
Edinburgh, I was unable to say anything respecting the condition 
of the seeds. Now, as I have examined the capsules, I may state 
that each was well filled with seeds, of which about one-fifth were 
embryonated. 
Secondly, I applied the pollinia of O. sphacelatum to the stigmas 
of six flowers of the O. graminifolium, from which I obtained one 
good capsule with one-fourth of embryonated seeds. I failed to 
effect a reciprocal cross by applying pollinia from O. graminifolium 
to the stigmas of O. sphacelatum, as all the flowers thus operated 
upon dropped early. 
Thirdly, I applied the pollinia of O. sphacelatum to the stigmas 
of O. ornithorhynchum, and from four flowers thus impregnated I 
obtained one capsule. On dissection I was disappointed by finding 
that it contained few seeds, and of these a very high percentage 
presented merely a loose transparent testa, entirely destitute of 
an embryo. I did not succeed in impregnating O. sphacelatum 
by pollinia of O. ornithorhynchum, though the capsules thus 
treated in several instances showed symptoms of swelling. 
Fourthly, I tried repeatedly to fertilize O. sphacelatum with the 
pollinia of O. altissimum, and also to reciprocally fertilize O. altis- 
simum by pollinia of O. sphacelatum, yet in both cases I utterly 
failed. It is here worthy of remark, as showing how completely 
independent the conjunctive capacity of two distinct species may 
be of their systematic affinities, that the O. altissimum and O. 
sphacelatum, which I have thus failed to cross, are nevertheless so 
closely allied as to have been regarded as conspecific, whereas in 
the previously given fertile unions of O. sphacelatum with O. divari- 
catum var. cupreum, O. graminifolium, and O.ornithorhynchum, there 
are great dissimilarities in the specifie characters. 
Fifthly, I impregnated a number of flowers on different plants of 
the O. sphacelatum with their own pollinia, yet in no instance did 
a single capsule swell. The only external signs the flowers afforded 
of being affected by the pollinia were the closing of the stigmatie 
orifice, twenty-four hours or so after their application, and the 
slightly earlier withering of the flowers. On the plant of O. spha- 
celatum, previously noticed as readily susceptible to fertilization by 
