Vol. 2] Gardner. — Cytological Studies in Cyanophyceae. 263 



The lines of modification are, first, the concentration of the 

 whole nucleus toward the center of the cell and the consequent 

 concentration of the chromatin ; and, second, the union of the 

 chromatin into a more or less continuous thread. The differen- 

 tiation seems to be proceeding toward the spireme formation 

 found in the dividing of the nucleus of the higher plants. Of all 

 the species of Cyanophyceae thus far worked upon, Fig. 1 repre- 

 sents the type in its simplest form. In this species the nucleus 

 occupies the larger part of the cell, and the chromatin is distrib- 

 uted throughout it in the form of disconnected irregular pieces. 

 Fig. 2 represents a modification of this in the direction of the 

 union of the chromatin into more of a continuous mass. Fig. 3 

 represents a modification in the concentration of the nucleus to- 

 ward the center of the cell. In Fig. 4 we see both greater concen- 

 tration of the nucleus and greater union of the chromatin. The 

 nucleus in Fig. 5 represents about the extreme in both directions. 

 It occupies a relatively small amount of space in the cell and is 

 usually, though not always, united into a single mass, much 

 branched, with free ends projecting. There may be smaller free 

 masses in addition to the large mass, which is not solid through- 

 out. Fig. 6 represents a nucleus with very irregular outline in 

 which the chromatin is in the form of thin irregular plates, 

 mostly united around the margin but discontinuous in the middle. 



Longitudinal views of Figs. 1, 3, 4, and 5 are represented by 

 Figs. 7a, 8, 10, and 9 respectively. 



These figures are all of comparatively short-celled species; 

 that is, relatively short as compared with the diameter of the 

 trichome. The cell of Fig. 1 is about 30/x in diameter and the 

 cells are from 3/x to 5/a long. In species whose cells are several 

 times longer than broad the nucleus is extended in the longitud- 

 inal direction, and has a tendency to arrangement of the chro- 

 matin into the form of threads somewhat united, and these are 

 oriented more or less parallel to each other, and parallel to the 

 long axis of the cell. Figs. 12, 13, and 17 represent such an ar- 

 rangement. 



Figs. 11, 24, 25, and 26 represent a still higher degree of dif- 

 ferentiation in the direction of a sharper separation of the cyto- 

 plasm and the nucleus. The chromatin is collected near the center 



