276 University of California Publications. [Botany 



formed some experiments with the view of ascertaining if pos- 

 sible the nature of these changes. The effect of being subjected 

 to long drought was first studied. A collection of Phormidium 

 uncinatum was made after it had been dry for five months. The 

 material was wetted and examined in this condition ; afterward 

 the aid of stains and fixing agents was resorted to. The results 

 showed that what I have since proved by experimentation, viz., 

 that a large percentage of the cells were in a resting condition 

 brought about by slow desiccation. A large number of hormo- 

 gonia had been formed, and these began to grow very rapidly, 

 soon crawling out of their sheaths. After a few days, more of 

 the material was stained, and the only change that had taken 

 place was the appearance of rapidly dividing cells. The chroma- 

 tin, instead of being drawn into the center of the cell, in many 

 cases now extended through a series of partially divided cells, or, 

 in case of a recently divided cell, it was still found close to the 

 cross-wall. So this sudden change from an aerial dry condition 

 in the direct sunlight (in which it had persisted for months) to 

 submergence in water and diffused light does not produce any 

 perceptible change in the structure of the cell contents nor in the 

 character of their reaction to stains. 



Still further to test the effect of change from an aerial to an 

 aqueous medium, living material of Oscillatoria sancta, found 

 actively growing on soil in a greenhouse, was placed in water. In 

 this instance there was not only a change from an aerial to an 

 aqueous environment, but also a sudden change in temperature. 

 The growth of the plants was not interfered with to a noticeable 

 degree, and the cytological characters remained unaltered. The 

 normal habitat of this species is of course not in a greenhouse, 

 but outside, where it is subjected to variation of light, heat, and 

 moisture. The same structure of the cell appears when these 

 plants from a normal habitat are stained. 



Symploca Muscornm withstood being dried up several times 

 without manifesting any cytological modifications. A change in 

 habit of growth occurs when this species is changed from an 

 aerial to an aqueous environment. In the air the filaments unite 

 into fascicles, somewhat cone-shaped, but in water they spread 

 out. 



