204 THE LIFE OF THE PLANT 



them, and within it the same protoplasm and cell-sap; 

 while in the middle, like a spider in its web, we find a 

 nucleus connected with the wall by very fine strands 

 of protoplasm. We can observe such a filamentous 

 weed in a drop of water under the microscope for 

 several hours, and even days, and submit it during 

 that time to different temperatures, and to varying 

 illumination. In this way we see, for instance, that in 

 the absence of light cells grow or rather elongate more 

 quickly than in the presence of light. Light has a 

 similar retarding influence on the multiplication of 

 cells : at all events under normal conditions, this pro- 

 cess takes place mainly and sometimes even exclusively 

 at night. Formerly investigators had to arm them- 

 selves with much patience : they either had to sit up 

 part of the night to observe one and the same cell, or 

 else to lay aside, in spirits of wine, specimen filaments 

 every hour or so, and subsequently observe the succes- 

 sive steps of the process in these different cells.^ Nowa- 

 days the same result may be reached in a far easier 

 way : when a vessel containing the weed is placed for 

 the night in a cool place like a cellar, the process of 

 multiplication is arrested till the next day, so that in 

 this way we can always take advantage of the more 

 pleasant hours of the day-time instead of the less pleasant 

 hours of night for observing the process in the same cell. 

 The process itself is very simple. It consists 

 in the division, the splitting into two of the contents of 

 a single cell. This happens in the following way : 

 when a cell has reached the stage of development at 

 which it divides, two outgrowths from the wall appear 

 projecting into the cavity of the cell (fig. 58, C, D). 

 The cells under investigation are cylindrical in form. 

 By making them rotate round a longitudinal axis by 



' Under continual artificial illumination division also takes place in the 

 presence of light. Evidently the light does not interfere directly with 

 division, but rather promotes the activity of the ceU in another direction. 



