ROOTS. 



107 



food supplies. 

 Therefore, pro- 

 cesses are devel- 

 oped which pene- 

 trate and absorb. 

 The mistletoe and 

 dodder are seed- 

 plants which have 

 this habit , and 

 both have such 

 processes (see Figs. 

 102, 103). This 

 habit is much more 

 extensively devel- 

 oped, however, in 

 a low group of 

 plants known as 

 the fungi. Many 

 of these parasitic 

 fungi live upon 

 plants and animals, 

 common illustrations being the mildews of lilac leaves and 

 many other plants, the rust of wheat, the smut of corn, etc. 



70. Root structure. 

 — In the lowest groups 

 of plants (algae, fungi, 

 and moss-plants) true 

 roots are not formed, 

 but very simple struc- 

 tures, generally hair- 

 like (see Fig. 104). In 

 fern-plants and seed- 

 plants, however, the 

 root is a complex 

 structure, so different 

 from the root-like pro- 



Fig. 103. A section showing the living connection 

 between dodder and a golden rod upon which it is 

 growing. The penetrating and absorbing organ (A) 

 has passed through the cortex (c), the vascular 

 zone (b), and is disorganizing the pith (p). 



Fig. 104. Section through the thallus of a liver- 

 wort (Marchantia), Bhowing the hair-like pro- 

 cesses (rhizoids) which come from tlu' under 

 surface and act as roots in gripping and ab- 

 sorbing. In the epidermis of the upper surface 

 a chimney-like opening is seen, leading into 

 a chamber containing cells with chloroplasts. 



