45 O THE AMERICAN NATURALIST. [Vol. XXXVI II. 



to the granular state. By the granular state we mean one in 

 which no fibrillse seem to be present, but instead the microsomata 

 are densely and homogeneously massed'. It is possible that such 

 microsomata form a closely packed network, but no such struc- 

 ture is visible under the microscope. The first appearance of 

 kinoplasm at prophase of mitosis is frequently the granular 

 condition. This ^ate is illustrated by such accumulations as 

 centrospheres and kinoplasmic caps and by the granular zone 

 that has been reported around the nuclei of some spore mother 

 cells. 



Granular kinoplasm becomes fibrillar probably by the arrange- 

 ment of the microsomata into a reticulum from which fibers 

 extend freely into the surrounding cytoplasm. These fibers 

 undoubtedly elongate during prophase, extending in various 

 directions. Some press against the nuclear membrane and when 

 this breaks down grow rapidly into the nuclear cavity. Of these 

 a portion extend from pole to pole and form the central spindle. 

 Others attach themselves to the chromosomes and lie either 

 among the central fibers or somewhat outside of the spindle 

 (mantle fibers). Still others may extend freely into the cyto- 

 plasm as astral rays from the pole of the spindle, a very com- 

 mon condition when centrosomes or centrospheres are present. 

 A contraction of the fibrillae, beginning with metaphase, is just 

 as characteristic of mitosis as their elongation during prophase. 

 The fibers attached to the chromosomes draw the latter to the 

 poles of the spindle. The central fibers in higher plants draw 

 away from the poles and give their substance to the cell plate. 

 The substance of contracted mantle fibers, with other kinoplasm 

 at the poles of the spindle, probably become distributed around 

 the group of daughter chromosomes so that they finally lie sur- 

 rounded by a sphere of kinoplasm. 



It does not seem as if we knew much more about the struc- 

 ture and activities of kinoplasm during mitosis than is indicated 

 in this cycle of change from a granular condition through a 

 fibrillar state back to the granular condition, with a period when 

 the fibers elongate and another when they contract. This with 

 few exceptions is the history for every mitosis. The exceptions 

 deal with peculiar conditions or structures. Thus, for example 



