14 



BOTANY 



FIQ. 3. Types of unicellular 

 plants ; A, B, Chlorococcum 

 sp? (X about 1000) ; B, two 

 individuals resulting from 

 division ; cr, chromatophore, 

 enclosing the pyrenoid, p; 

 n, nucleus; C, a Desmid, 

 Euastrum elegans (X 300) ; 

 D, 8-celled colony of Pedi- 

 astrum (x 500). 



phore. These green Flagellata are not necessarily naked cells, but 



may show the characteristic cellulose membrane, which is perforated 



to permit of the protrusion of the cilia. 



In all but the lowest forms of plants, 

 the power of locomotion is lost, except 

 in the reproductive cells, and the develop- 

 ment of a continuous cellulose membrane 

 prevents any protrusion of the protoplasm 

 outside the cell, and the vegetative cells 

 are normally stationary. Such cells pre- 

 sent a strong contrast to the animal-like 

 green Flagellata and motile Bacteria. 



Most unicellular plants are either oval 

 or globular the natural form a free cell 

 assumes where pressure is alike in all 

 directions. There are, however, many 

 exceptions to this, and the single cell may 

 show much variety in form and size. 

 Sometimes the cell is so minute as to be 

 barely visible with the very high powers 

 of the microscope ; on the other hand, 



some of the cells, or more properly ccenocytes of the peculiar group, 



the Siphoneee, may be ten centimetres or more in length. Of the 



strictly unicellular 



forms, probably the 



Desmids (Fig. 3, C) 



offer the greatest 



known variety of 



form. In the Sipho- 



nese, like Caulerpa 



(Fig. 4), the extraor- 

 dinary differentia- 

 tion of the coenocyte 



is perhaps better 



comparable with that 



of a multicellular 



plant-body in which 



the division walls 



are suppressed, as the 



multinucleate proto- 

 plasm is made up 



of many energids. 



These ccenocytes, or 



similar multinucleate complexes, are commoner in animals than 



in plants. 



FIG. 4. Caulerpa plumaris, a non-cellular plant or 

 coenocyte, showing differentiation into stem, root, and 

 leaf ; x, growing point ; natural size. 



