330 
functions of the plant body resolve them- 
selves into the functions of the unit of that 
body. Jn every organ, however simple or 
however complex, we recognize the individ- 
ual protoplast as the unit of work as well 
as the unit of structure. Each, enclosed in 
the armor-like wall which it has formed for 
itself, though hampered in its movements, 
is able to carry on the chemical and phys- 
ical processes which constitute life with- 
out notable hindrance. Within the proto- 
plast, for which Sachs uses the expressive 
though unnecessary word energid, there go 
on certain changes that can be observed 
with the microscope. These changes we look 
upon as the index of the invisible ones 
whose significance we seek to understand. 
It is natural, therefore, that the closest 
scrutiny should be made of the observable 
changes which take place within the cell. 
This minute study began in the attempt to 
ascertain how the living protoplasm con- 
structed the wall with which it jackets it- 
self. Every difference in composition which 
involved an optical alteration in the trans- 
mission of light, and so beeame visible, has 
been studied with the utmost care. 
Later, attention was attracted to the di- 
vision of the various independent proto- 
plasmic organs within the cell body. Some 
of these have been found to be relatively 
simple. The division of the nucleus, how- 
ever, has shown a complexity and at the 
same time a regularity which has chal- 
lenged the minutest investigation and has 
made it the center of the greatest interest. 
So complex a series of changes, recurring 
with such regularity, argues an importance 
for both function and phylogeny which 
has made students eager to ‘discover the 
secret. Therefore, within the last few years 
the behavior of the nucleus and of its differ- 
ent parts has been under study in all 
groups of plants with an exactitude never 
before dreamed of. Thus cytology has 
come to be an almost independent line of 
SCIENCE. 
[N. S. Von. X. No. 245. 
investigation. It is to be feared, how- 
ever, that in many cases its exaltation 
has led students to mistake its real pur- 
pose and to consider it an end in itself. 
The visible processes within the cell 
will have little meaning unless they are 
looked upon as the mere index of its work. 
Unless the details of mitosis, for instance, 
are interpreted in the light of function or 
phylogeny they will certainly be misinter- 
preted or will be meaningless. It is be- 
coming a question whether we have not 
overestimated the importance of slight dif- 
ferences in nuclear phenomena and whether 
further knowledge can be expected from a 
study of the visible processes within it. 
At the same time decided progress is to be 
hoped for in a more intimate chemical 
knowledge of the substances composing the 
nucleus, as to their chemical constitution 
and their relation to chemical reagents, 
such as stains and fixing fluids, rather than 
in repeated counting of chromosomes and 
multiplied observation of the details of 
prophase and anaphase. 
I have now discussed the chief features 
of plant physiology in which notable prog- 
ress has been making during the last 
decade. The great advances in plant 
chemics and physics; the progress in the 
investigation of causes of plant form; the 
widening ideas of the property of irritabil- 
ity ; the investigation of the social relations 
of plants, and the minute study of cell 
action in spite of their diversity, have one 
great end in view. This is nothing less 
than the solution of the great problem— 
the fundamental problem—of plant phys- 
iology,as of animal physiology. The secret 
which we must discover, the dark recess 
toward which we must focus all the light 
that can be obtained from every source, 
is the constitution of living matter. Hn- 
trenched within the apparently impregnable 
fortress of molecular structure this secret 
