THE STRUCTURE OF PROTOPLASM 
283 
I have illustrated my viewpoint as to protoplasmic structure rather 
fully by the cases of the elaioplasts, plastids, and chondriosomes. The 
recent literature on these structures seems to me especially suggestive of 
the tendencies which are promising and of those which are reactionary in 
present-day cytological literature. 
The conceptions of cytologists as to the chromosomes as units of cell 
structure are much more definitely fixed as a result of the vastly greater 
amount of attention which has been devoted to them. It is of interest to 
note that cytologists have devoted their attention almost entirely to the 
phenomena of reproduction and heredity. The phenomena of direct and 
indirect nuclear and cell division in asexual reproduction on the one hand, 
and of chromosome reduction and nuclear and cell fusion in connection 
with sexual reproduction on the other, have furnished such a wealth of 
easily accessible data that the processes of cell metabolism, growth, and 
irritability have been relatively neglected. 
In the same way those physiologists who have used principally the 
methods of chemical analysis and physical measurements have found just 
these problems which the cytologist has neglected the more accessible. 
There has grown up thus an interesting division of the field according to 
the methods of study used by the investigator into cellular physiology or 
cytology, dealing largely with reproduction, and what is generally known 
as plant physiology, dealing quite as exclusively with metabolism, growth, 
and irritability. This might seem to indicate that the physiology of repro- 
duction is a negligible field. At least one recent text-book of plant phys- 
iology states that the subject of reproduction has been adequately treated 
under the head of morphology. Such vagaries of viewpoint and opinion 
may safely be left to the future for correction, but it is the conspicuous fact 
that cytologists have largely concentrated their attention upon the phe- 
nomena of reproduction with the result that unquestionably the chromo- 
somes are the best known bodies of their size in the whole field of science. 
The attempt to question the validity of the evidence for the existence of 
these structures in the living cell and to class them and other cell structures 
as products of fixation, staining, etc., has broken down completely. The 
older studies of Strasburger on division figures in living cells have been 
confirmed and extended by Lundegardh and others. The essential char- 
acteristics of the chromosomes as to their form, size, and position in the cell 
and with reference to each other are recognizable in cells that are still alive 
and going through the processes of division. Their persistence in the resting 
condition of the cell in many plants either quite unchanged or as the so-called 
prochromosomes has been adequately demonstrated in fixed and stained ma- 
terial by Rosenberg, Overton, and others. Leaving aside the doubtful cases 
of the bacteria, blue green algae, and perhaps some protozoa, it is well nigh 
universally agreed that every cell has its specific complement of chromosomes 
quite definite in number, size, and perhaps in relative position in the cell body. 
