36 



PLANT LIPE. 



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 Ijladders, and the hair-pits (fig. 



Fig. 46. — Several plants of Lessonia, sliowinv,' trcr-like thallus and branched rhizoids 

 attaching the plants to rocks. -^^ natural size. — .Aftei- L.e IMa-uit & Decaisne. 



43) with which many species arc covered, would reveal slill 

 other modes of dilTercntiation of cells from those of the 

 apical mcristem. Accompanying tlic change of form is 

 always specialization of function, which we can interpret 

 only in a very imperfect fashion irom our own standpoint. 



