1900] CHANGE OF FORM IN GREEN ALG& : 295 
change in solution strength, and sent out long filaments from 
the original palmella masses ( figs. 7, 75; 16). Also the palmella 
cells produced numerous zoospores. These germinated, as pre- 
viously described, to produce, not the parent form, but the 
widely different filamentous one. Conversely, it was found that 
if filaments, produced as above, and growing healthily in a 0.2 
per cent. or 0.25 per cent. nutrient solution, were changed to 
one of I per cent., 1.5 per cent., or 2 per cent. strength, the 
tesponse was scarcely less well marked than in the other case, 
the cells of the filaments soon became spherical, and changed to 
the palmella form by dividing in both longitudinal and transverse 
planes (jigs. 4, 5). In the strong solutions few or no zoospores 
were produced. Where a few were produced they changed, 
either directly or after the first or second division, to the palmella 
With these two facts in view the attempt was made to deter- 
mine where, in this change of solution strength, lies the neces- 
sary stimulus for the production of the corresponding change of 
fom. A stimulus arising from a change of solution strength 
(always retaining the same salts in the same proportion) may 
be of any one of three different natures. (1) It may be of a 
chemical nature : z. @., it may be due to a change in the amount 
of salts with which the organism is supplied. This implies 
three possibilities : (2) the plant may be affected by the increase 
jaa in all the inorganic salts. (4) Again when such 
aia is made it may be the change in amount of a single salt, 
rad Pedetum nitrate, to which the plant responds. There are 
Ur possibilities under this head, one for each of the four salts 
*¢. (c) Again, it may be possible that neither of the pre- 
Cedi me f the 
to Ry Suppositions is true, but that the response 1S due, not | 
k the changes together, nor to any one alone, but to @ come. 
aah or three of them. For example, it pers 
— i. € amount of potassium phosphate together wit! Le 
— €xce ti Tutrate, which acts as a stimulus. We know 7 
._ bit in very weak solutions, these two salts react chem- 
Y "pon each other, so that it is at least conceivable that am 
