CYTOLOGY. In recent years another definite Yield of botanical research has been developed, which deals exclusively with the problems of the cell, and is called Cytology (q.v.). It is related to anatomy in that it deals with cells. which in their aggregation form the tissues that are the subject of anatomy. At the same time, it studies cells from the standpoint of mor phology, since it is concerned with cell-organs. their origin and mutual relationships; while it also has its distinct association with physiolo gy, inasmuch as the functions of its organs fur nish the ultimate problem of the cell. It is through cytological investigation that the tech nique of research with the microscope has been developed so greatly. The discoveries in methods of killing material, in imbedding. sectioning. and staining, have brought to view structures which were invisible to the observers of a few years ago.
The principal problems of cytology at present are the structure and activities of protoplasm, the life-history of plastids t protoplasmic organs of the cell. of which chlo•oplastids, the green color-bodies of leaves, are examples), the struc ture and function of the nucleus (an essential and permanent organ of the living cell). the reduction of chromosomes (bodies which enter into the structure of the nucleus). The origin and development of the achromatic figure (a peculiar spindle-shaped body which appears in connection with a dividing nucleus), the centro some (a cell-organ supposed to be prominently concerned in the division of the nucleus), the cell-wall. the development of the sex-cells, fertilization. the embryo, and the problem of heredity.