20 OUTLINES OF PLANT LIFE. 



2. Observe form and particularly the abundant branching. Can a 

 single main axis be traced ? How many branches arise at one point ? 



Fig. 20. — A young plant of Vaucheria^ developing from the spore, A^ mature spore ; 

 B^ the same after germination has. begun ; C, plant further developed from spore, sp^ 

 ■with growing apex, j, and rhizoid, 10, by which it attaches itself to the mud. The 

 chloroplasts are numerous and close together next the wall on all sides. Magnified 28 

 diam, — After Sachs. 



26. Partition walls unnecessary. — Many algse, while ex- 

 ternally like others, which are divided into true cells, have not 

 the units of structure separated by cell-walls. In Vaucheria, 

 for example, the whole of the vegetative body forms a single 

 chamber, in which lies the undivided 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 the partition walls are not formed. 



27. External segmentation. — A plant body of this con- 

 struction may attain considerable size and complexity, as in 

 Caulerpa (fig. 21),* even to mimicking, upon a small scale, 

 the form of leafy plants. In such cases the external walls 

 become considerably thickened, and across the chamber, from 

 one side to the other, run irregular bars of similar material 

 which act as braces to prevent the collapse of the outer walls 

 (fig- 22). 



In Caulerpa, particularly, a high degree of development as 

 to external form is reached (fig. 21). There is a stem-like 



* Note carefully the scale of the figures. 



