PROTOCOCCUS VIRIDIS. 25 



11. The cell multiplication: examine various specimens 

 and trace the successive stages in the division of a 

 single cell to form a cell family. 



12. Illustrate the cell multiplication by drawings. 



ANNOTATIONS. 



Protococcus is a unicellular plant, for each cell 

 performs individually the various functions pertaining 

 to plant life ; and this is true whether the cells remain 

 single or become associated into small families. 



The cell is the unit from which all plants, however 

 complex, are built up. 



The most essential part of the cell is the protoplasm, 

 a colorless semi-fluid substance, which in this instance 

 is masked by the green chlorophyll. It is the only 

 really living, active agent in this, as well as in all other 

 plants. Its presence here is made manifest by the 

 characteristic yellowish-brown color given by iodine. 



The nucleus (see fig. 9 n) is a special form of the pro- 

 toplasm to be seen in most plant-cells. As its division 

 usually precedes that of the cell, it has generally been 

 regarded as in some way necessary to the latter pro- 

 cess. The investigations of Schmitz, Strasburger 7 and 

 others go to show, however, that the two processes 

 are distinct, and that the nucleus, instead of being 

 related to cell division, holds an intimate and probably 

 essential relation to the life of the protoplasm. 



The protoplasm takes on another form in the chlor- 

 ophyll bodies 8 (see fig. 9 c). These consist of a proto- 



7 Zellbildung und Zelltheilung, p. 371. 



8 Cf. Strasburger, Das botanische Practicum, p. 350 ; Schmiu, 

 Chromatophoren der Algen. 



