Vol. 2] Gardner. — Cytological Studies in Cyanophyceae. 277 



The effect of changing the concentration of the liquid me- 

 dium was tried. Lyngbya aestuarii growing in salt water was 

 transferred from this into fresh water, also into distilledjwater. 

 Material was studied before and after the change, and on com- 

 parison the structure of the protoplast presented no unusual 

 modification. This species will survive the change from salt to 

 fresh water for many months, and even a surprisingly long time 

 when changed to distilled water. 



The rate of growth may be influenced in various ways. Other 

 things being equal, the amount of light is a prominent factor in 

 influencing cell division. If young, actively growing material be 

 placed in the dark, growth proceeds very slowly, and after a few 

 days or weeks, depending upon the species, will discontinue al- 

 most entirely. In diffused light growth proceeds more rapidly 

 than in the dark, and in direct sunlight the maximum growth 

 takes place. This is doubtless due in a large measure to nutri- 

 tion rather than to the direct action of light rays. As a contin- 

 uous habitat, however, some species prefer diffused light rather 

 than direct sunlight. The comparative activity of cultures placed 

 in direct sunlight and of those placed in diffused light or in the 

 dark may usually be detected within a few minutes. Those 

 placed in direct sunlight will be seen to be giving off more oxygen 

 than the others. This collects and forms bubbles, which become 

 entangled and held fast in the mass of filaments, in many cases 

 soon buoying them up to the surface of the water. This has al- 

 ready been alluded to under methods of obtaining clean material. 

 The metabolism of those in diffused light or in darkness is usu- 

 ally not sufficiently rapid to cause the accumulation of gas, which 

 is absorbed by the water as fast as given off. 



It is quite remarkable how tenacious of life some forms are 

 when placed in the dark. A culture of Aphanothece which was 

 in fair vegetative condition was placed in a dark chamber arid 

 supplied with enough water to keep it moist for sixty days. It 

 then dried up and remained dry and brittle for fifteen more 

 days. It was again wetted and some of the material stained, 

 when it was found that a few cells were still dividing and that 

 very few had died. The nucleus had become somewhat more con- 

 centrated into the center of the cell, and there were fewer gran- 



