266 University of California Publications. [Botany 



These, like the spores, rest for a time until favorable conditions 

 arrive, such as proper temperature, moisture, food, etc., then they 

 resume growth and build up new trichomes. During this time 

 they must be quite at rest. 



(a) THE DIVIDING NUCLEUS. 



The division of the nucleus in the Diffuse type is unmistak- 

 ably amitotic. Whether in the short-celled form represented by 

 Oscillatoria margaritif era (Fig. 7) or in a long narrow-celled 

 form represented by Oscillatoria splendida ( Fig. 17 ) , the process 

 is very much the same and quite simple. The chromatin is dis- 

 tributed quite uniformly throughout the nucleus in the resting 

 cell. It presents no peculiar characters or modifications in form 

 or structure during cell division that do not exist in the resting 

 cell with the exception in many cases of a constriction in the 

 middle as if the ingrowing cell-wall were actually pressing the 

 chromatin toward the center before dividing it. It is impossible 

 to say at present what causes the chromatin to separate. The 

 separation always takes place at the outer margins first and pro- 

 ceeds toward the center of the cell. In no case have I noticed the 

 whole mass separating simultaneously. Whether the ingrowing 

 cell-wall plays any role in the process or not, it is never very far 

 from the edge of the divided chromatin. Fig. 7 represents cells 

 in various stages of division : a represents a resting cell, b one in 

 which the division has proceeded only a short distance, c one al- 

 most divided, and d a complete division. The chromatin in these 

 cells is represented in greater abundance than exists in the greater 

 number of cells in this species. An instructive series is shown in 

 Fig. 12, in which a represents the first stage in the series. The 

 only sign of division is the beginning of the laying down of the 

 ring-shaped cross-wall. No evidences of nuclear division are yet 

 manifest : b shows the wall grown into the chromatin which is be- 

 ginning to separate ; c represents a stage in which the entire mass 

 of chromatin has separated except a single strand in the center. 

 In Fig. 18 may also be seen the same condition of chromatin 



