LINEAR AND SUPERFICIAL AGGREGATES. 23 



structure separated by cell-walls. In Vaucheria, for example, 

 the whole of the vegetative body forms a single chamber, 

 in which lies the united protoplasm, corre- 

 sponding to many cells, as shown by the 

 numerous nuclei which are distributed through 

 it. The external walls of the cells are formed, 

 but, when the nuclei divide as growth proceeds, 

 the protoplasm does not divide, and the septa 

 or partition-walls are not formed. Such an un- 

 septate company of cells is called a coenocyte. 



In the cladophoras (fig. 29) some of the 

 normal divisions are complete, while others 

 are only nuclear divisions. Consequently the 

 cladophoras seem to be a filament of true 

 cells, but in reality each apparent cell is a 

 coenocyte, as shown by the several nuclei in 

 each (fig. 30). 



29. External segmentation. — A plant 

 body of this construction may attain con- 

 siderable size and complexity, as in Caulerpa 

 (fig. 31) and Acetabularia (fig. 32),* even to 

 mimicking, upon a small scale, the form of 

 leafy plants. In such cases the external walls 

 become considerably thickened, and across ¥lG - 2 9-a single 



J ' plant of Clado- 



the protoplasm and its large vacuoles, from phora, showing 



1 ** . profuse monopo- 



one side of the chamber to the other, run £ al branching. 



7 Natural size. — 



irregular bars of cellulose which act as braces After Hauck. 

 to prevent the collapse of the outer walls (fig. 33). 



In Caulerpa, particularly, a high degree of development 

 as to external form is reached (fig. 31). There is a stem- 

 like axis, v-s, creeping in the mud, which bears green leaf- 

 like branches, b, on one side and clusters of colorless root- 



* Note carefully the scale of the figures. 



