36 



PLANT LITE. 



arises thus a cortex, as the outer dense part is called, and a 

 medulla or pith, as the mucilaginous and apparently isolated 

 central cells and filaments are called. At the bladders, the 

 pith becomes filled with air and other gases. 



44. Special functions. — Complete examination of all parts, 

 the disk of attachment, the bladders, and the hair-pits (fig. 



Fig. 46. — Several plants of Lessonia, showing tree-like thallus and branched rhizoids 

 attaching the plants to rocks, j B natural size.— After I .<• Maout & Decaisne. 



43) with which many species are covered, would reveal still 

 other modes of differentiation of cells from those of the 

 apical meristem. Accompanying the change of form is 

 always specialization of function, which we can interpret 

 only in a very imperfect fashion from our own standpoint. 



