540 
phenomena of irritability and growth are 
closely related to the physics of plant life, 
they are essentially morphologic, and it is 
here especially that we have a voluminous 
literature based strictly on the inductions 
gained by experimentation, and for which 
we have chiefly to thank the plant physiol- 
ogists. 
If we were to write the full history of ex- 
perimental morphology in its broadest as- 
pects we could not omit those important 
experimental researches on the lower plants 
in determining the ontogeny of polymorphic 
species among the alge and fungi which 
were begun so ably by DeBary, Tulasne, 
Pringsheim and others and carried on by a 
host of European and American botanists. 
The tone which these investigations gave to 
taxonomic botany has been felt in the study 
of the higher plants, by using to some ex- 
tent the opportunities at botanic gardens, 
where plants of a group may be grown 
under similar conditions for comparison, 
and in the establishment of alpine, subal- 
pine and tropical stations for the purpose of 
studying the influence of climate on the 
form and variations of plants, and in study- 
ing the effect of varying external condi- 
tions. 
While experimental morphology in its 
broadest sense also includes in its domain 
cellular morphology and the changes re- 
sulting from the directive or taxic forces 
accompanying growth, it isnot these phases 
of morphology with which I wish to deal 
here. 
The question is rather that of experi- 
mental morphology as applied to the in- 
terpretation of the modes of progress fol- 
lowed by members and organs in attaining 
morphologic individuality, in the tracing 
of homologies, in the relation of members 
associated by antagonistic or correlative 
forces, the dependence of diversity of func- 
tion in homologous members on external and 
internal forces, as well as the causes which 
SCIENCE. 
[N.S. Von. VI. No. 145. 
determine the character of certain paternal 
or maternal structures. I shali deal more 
especially with the experimental evidence 
touching the relation of the members 
of the plant which has been repre- 
sented under the concept of the leaf as 
expressed in the metamorphosis theory of 
the idealistic morphology. The poetry and 
mystery of the plant world, which was so 
beautifully set forth in the writings of 
Goethe and A. Braun, are interesting and 
entrancing, and the poetic communication 
with nature is elevating to our ethical and 
spiritual natures. But fancy or poetry 
cannot guide us safely to the court of in- 
quiry. We must sometimes lay these in- 
stincts aside and deal with nature in a 
cold, experimental, calculating spirit. 
The beginnings of experimental mor- 
phology were made about one century ago, 
when Knight, celebrated also for the im- 
pulse which he gave to experimental physi- 
ology, performed some very simple experi- 
ments on the potato plant. The under- 
ground shoots and tubers had been called 
roots until Hunter (77) pointed out the 
fact that they were similar to stems. 
Knight tested the matter by experiment, 
and demonstrated that the tubers and un- 
dergound stems could be made grow into 
aérial leafy shoots. This he regarded as 
indicating a compensation of growth, and 
he thought farther that a compensation of 
growth could be shown to exist between the 
production of tubers and flowers on the 
potato plant. He reasoned that by the pre- 
vention of the development of the tubers 
the plant might be made to bloom. An 
early sort of potato was selected, one which 
rarely or never set flowers, and the shoots 
were potted with the earth well heaped up 
into a mound around the end of the shoot. 
When growth was well started the soil was 
washed away from the shoot and the upper © 
part of the roots so that the plant was only 
connected with the soil by the roots. The 
