SEPTEMBER 8, 1899. ] 
plant has led to many fruitful investigations 
during the past decade. The ingenious ap- 
plications of plaster jackets for mechanical 
restraint of growth has thrown light not 
only upon the mechanical forces which can 
be exerted by growing organs, but casts a 
side light upon the difficult problem of the 
mechanics of growth. Researches upon 
the mechanics of curvature induced in 
growing organs by stimuli have been made 
by several observers, without obtaining, 
however, the concordant results which are 
to be desired. The subject, therefore, re- 
quires further study. 
A satisfactory hypothesis as to what hap- 
pens when an irritable organ is stimulated 
is still a desideratum. Is irritable proto- 
plasm merely ina state of extraordinary la- - 
bility, and does the stimulus initiate the 
decomposition of the protoplasm or of some 
unstable substance which it has produced? 
If this is true the metabolism of irritable 
organs which have been strongly stimulated 
ought to be different from that of similar 
but quiescent organs, and different products 
may be expected. One of the most note- 
worthy advances in this direction seems to 
be the discovery by Czapek (unfortunately 
we have had as yet only a preliminary 
paper) that roots after being geotropically 
stimulated contain notable amounts of re- 
ducing substances as compared with un- 
stimulated roots which contain oxidizing 
substances instead. 
Again, the transmission of impulses in 
plant tissues has been under frequent study. 
Haberlandt’s seemingly well-founded con- 
clusions regarding the transmission of im- 
pulses in Mimosa have proved untenable in 
the light of MacDougal’s experimeuts, 
which also seem to shut out the possibility 
of the action of living protoplasm. The 
travelling of an impulse through a zone of 
dead cells is so marvellous that we are 
tempted to discredit the evidence of our 
senses, but that it occurs cannot be 
| SCIENCE. 
O21 
doubted. Thus, again, the discordant re- 
sults of competent observers compel us to 
say that as good as nothing is now known. 
ECOLOGY. 
Within the past decade what may be 
considered a new division of plant phys- 
iology has been organized and has entered 
upon a development whose future extent 
and importance cannot yet be fully esti- 
mated. 
Like every apparently new departure, itis 
an evolution from the old. Though its rise 
has been phenomenal, many of its facts and 
principles have long been known. At the 
meeting of the Madison Botanical Congress 
of 1893 the word ecology was almost new to 
American ears, and doubtless some present 
at that Congress were surprised at the in- 
troduction of a resolution on so unimpor- 
tantasubject. Theadoption of a name and 
preferable form of spelling for the new 
science, however, has been very useful in 
unifying the practice of American writers, 
and is a good illustration of the beneficial 
effect of a formal agreement on a matter of 
usage. 
In the last century the relations of plants 
to insects were studied and Christian Con- 
rad Sprengel’s ntdeckte Geheimniss der 
Natur was a pioneer work in this subject. 
But Sprengel’s work was destined to be 
forgotten for many years, and the further 
study of these interesting adaptations for 
the pollination of plants by insects was only 
revived by the prolonged observations and 
ingenious experiments of Charles Darwin. 
Since his time the work has been taken up 
vigorously and knowledge enormously ex- 
tended by Muller, Ludwig, Delpino, Mc- 
Leod, Robertson and a host of others. 
The controlling influence of soil and cli- 
mate upon the distribution of plants was 
also recognized and measurably understood 
long ago. In the classical works upon 
geographical distribution, such as Grise- 
