606 
ive researches. Dr. Humbert carried out 
experiments in the speaker’s laboratory in 
which the capsules of a pure line of a wild 
plant Silene noctiflora were injected with 
the solutions used by Dr. MacDougal, and 
although the number of plants handled 
(about 15,000) was apparently as great or 
greater than was used in MacDougal’s 
experiments, no mutations were found in 
the treated plants which were not also 
found in the untreated or check plants. 
Some observations and experiments are 
recorded in literature which indicate that 
mutilations or severe injury may induce 
the development of mutations. Most note- 
worthy among such observations are those 
of Blaringham, who by mutilating corn 
plants in various ways, such as splitting 
or twisting the stalks, apparently produced 
variations which bred true without reeres- 
sion and which he described as mutations. 
My own observations on the great fre- 
quency of striking bud variations on re- 
covering trunks of old citrus trees in 
Florida, following the severe freeze of 
1894-5, also furnished evidence in sup- 
port of this theory. 
In general, it is assumed that in hybridi- 
zation we are dealing merely with charac- 
ters already present and that new charac- 
ters which appear are due to the different 
reactions caused by new associations of unit 
characters in their mutual effect on one 
another. It is, however, possible that new 
unit characters may result from the com- 
mingling of the different hereditary units 
which are to be considered as mutations 
rather than new combinations. As is well 
known, Weismann long ago advanced the 
hypothesis that valuable variations in evo- 
lution were due to the commingling of 
protoplasms from different parents having 
different hereditary tendencies, a process . 
which he ealled ‘‘ amphimixis.’’? He did 
not have in view, however, the formation 
SCIENCE 
[N.S. Vou. XXXV. No. 903 
of new unit characters as distinct from new 
combinations. 
The most marked case known to the 
speaker, of the appearance of a new char- 
acter which was apparently caused by the 
stimulation of hybridization, is the devel- 
opment of a marked spur or horn on the 
lip of a hybrid Calceolaria. This occurred 
among a series of hybrids between a her- 
baceous and a shrubby species made by 
Professor Atkinson and Mr. Shore, of the 
botanical department at Cornell University. 
One or two tapering horns about an inch in 
length and from 2 to 4 millimeters in diam- 
eter at the base, spring from the upper sur- 
face of the large corolla lip and grow erect 
to its surface. No such character, so far as 
ean be learned, is known in the Calceolarias 
and it would seem to have been caused by 
the hybridization. It ean not, apparently, 
be considered as a combination of any of 
the known characters of the species con- 
cerned. 
Such apparently new characters appear 
rather commonly among large batches of 
hybrids, and while there is little evidence 
available on the subject, I am inclined to 
believe it will be found that hybridization 
may stimulate the production of new unit 
characters, which mendelize with the pa- 
rental types. 
While the evidence at our command re- 
garding the artificial production of muta- 
tions is not yet sufficiently exact and trust- 
worthy to enable us to draw definite con- 
clusions and formulate recommendations 
for practical breeders, it may be stated 
that this is apparently one of the most 
profitable lines of experimentation for the 
immediate future. 
Thus far I have only incidentally dis- 
cussed hybridization and the advance of 
our knowledge in this direction. The scope 
of this address will not allow of an ade- 
quate treatment of this subject and it ap- 
