LivixGSTON : Chemical stimulation of a green alga 3 



resume of the previous results is here given. In nutrient media 

 whose osmotic pressure is from 323.7 cm. to 647.4 cm. of mer- 

 cury, the alga appears as groups of spherical cells with thickened 

 and somewhat gelatinous walls. Multiplication takes place rather 

 slowly, cell-division occurring in all directions, and the daughter 

 cells immediately become spherical, so far as this is not prevented 

 by adjacent cells. Often this process of rounding off results in the 

 entire separation of cells, so that a culture of this sort usually 

 exhibits numerous free cells of perfectly spherical form. In 

 weaker solutions, whose pressure is below 161. 8 cm. of mercury, 

 the daughter cells elongate into branching filaments composed of 

 cylindrical cells and having the typical appearance of the smaller 

 forms of the genus Stigeoclonimn. Growth is more rapid here 

 than in the strong solutions. If filaments are transferred to a 

 strong solution their cells round up and often separate, thus pro- 

 ducing the other form, and growth continues in the manner first 



F 



described. In the weak solutions zoospores are formed in great 

 numbers and germinate to form filaments ; in the strong solutions 

 they are not formed at all, and if transferred to such media they 

 fail to germinate, many of them, however, passing by direct 

 enlargement to the conditions of free spherical cells which later 

 behave in accordance with the pressure of the medium, as outlined 

 above. The biciliate zoospores are produced by simple segmenta- 

 tion of the entire cell-contents, which are freed by a final bursting 

 of the sporangium wall. 



A resting zoospore and several stages in the germination of 



r w 



these bodies are shown at a, fig. i \ at ^ is shown a more mature 



E 



filament, as these normally occur floating on the surface of the 



weak solution ; while at c is shown a form with more crowded 



branches, which is usually exhibited on the bottom of the culture 



dish, where air has not such free access. The spherical form, 



known usually in such algae as the palmella form, is shown in 



fig> 2. The groups of cells at a and c have developed from filaments 



which were transferred from a weak to a strong solution. The 



filamentous form is still to be seen in both groups, although it has 



well nigh disappeared in the lower. At b are some free cells in 



process of division which would result in groups of the palmella 

 form. 



