Igor] PHYSIOLOGY OF POLYMORPHISM IN ALGAE 297 
probably due to the poisonous action of some of the electrolyte 
ions used. To determine, if possible, what this action may be, 
will be the object of further research. 
The same culture may be made to change its form several 
times in sugar solutions just as in mineral solutions, by adding 
water or allowing it to evaporate. Nearly all the cultures made 
in sugar solutions have been controlled by others made at the 
Same time in mineral solutions, and the control cultures have 
not deviated at all from those discussed in my previous paper. 
Further, healthy material taken from sugar solutions behaves in 
water and in mineral solutions precisely as though it had been 
grown in a mineral solution. 
2. MIXED SOLUTIONS. 
These solutions contained both sugar and mineral salts. The 
response of the alga to the weaker ones is the same as though 
they were composed either of sugar alone or of salts alone. For 
the stronger solutions the same is true of the filamentous form. 
But the palmella form gives something of its characteristic 
response to sugar or electrolytes, according as one or the other 
of these substances predominates. However, this was not very 
well marked in the experiments. In general, the plant behaves 
in the same manner in a mixed solution as in a simple one. 
2. POROUS PLATE CULTURES. 
These were made on unglazed porcelain, such as is used in 
chemical work. A piece of plate four or five centimeters square 
was laid on the bottom of the culture dish, and sufficient solu- 
tion was poured over to stand within a millimeter or two of the 
upper surface of the plate. Thus the plate was saturated, but 
no free liquid was upon its surface. The alga cells were placed 
upon the plate and the whole was covered as usual. The results 
of these cultures are perfectly uniform, and are exactly what 
would have been expected. The osmotic pressure of the solu- 
tion which saturates the plate determines the response of the 
plant. Typical results from the series of plate cultures are pre- 
sented in table IV. The abbreviations are those used in tables 
