1 86 Macfarlanc — 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) Morphological Cytology. — 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 var^^-ing size. Like diversity characterizes 

 higher cell types. It seems premature, therefore, to attach 

 too much importance as yet to structural differences in ecto- 

 and endo-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 



