186 Macfarlane—Current Problems 
morphological cytology, (b) physiological cytology, (c) experi- 
mental cytology, (d) ecological cytology, (e) evolutionary 
cytology, and (f) taxonomic cytology. As in all natural 
systems of classification no one of the above is sharply 
demarcated from another, so that in attempting to treat of 
each there must of necessity be an overlapping. 
(a) MorpHoLocicaL CytTotocy.—Account might here be 
taken not merely of the resting and dividing cell, but of 
many problems relating to food products. I propose merely 
to touch upon the structure of the active cell, and in this the 
living protoplasm claims first attention. Though considerable 
emphasis has been laid on differentiation into zones, it seems 
still a very doubtful question how far we should attempt to 
speak morphologically of ectoplasmic and endoplasmic layers. 
Appearances often strikingly suggest such. The creeping 
“feeling” colorless margins of a living Myxomycete, or the 
same when fixed and stained, contrast strongly with the 
highly granular enclosed mass, but the extremely fine motile 
layer of protoplasm, which circulates immediately within the 
cellulose membrane of Spirogyra, and which is so clearly 
observed when the cell is dividing, encloses and carries along 
many granules of varying size. Like diversity characterizes 
higher cell types. It seems premature, therefore, to attach 
too much importance as yet to structural differences in ecto- 
andendo-plasm. But in much of the recent literature on cell 
structure and karyokinesis there is a growing tendency to 
recognize a fine system of radiating, and at times interlacing, 
“kinoplasmic”’ threads traversing the protoplasm. These 
threads, according to some authors, are peculiar to it, or are 
continuous with certain threads of the nucleus, in the resting 
or dividing state according to others. Three years ago, before 
the American Society of Naturalists I spoke of a fine net- 
work, containing chromatin substance, as being present in 
various plant cells distributed through the protoplasm and 
