116 



MINUTE STRUCTURE OF THE ROOT. 



351. Parasitic roots, 1 or those which fasten themselves for 

 nourishment on other plants, are so much modified by the pecul- 

 iar conditions under which they live, that they require special 

 mention. Their structure can be best understood by a section 

 through the root of Cuscuta. 



Here there is no central cylinder, properly so called, nor is 

 there anything answering to the root-cap. The cortex is regarded 



as reduced 

 to a pilifer- 

 ous layer, 

 since some 

 of its cells 

 are pro- 

 longed to 

 form a fasci- 

 cle of long 

 hairs in inti- 

 mate rontm-t 

 with the tis- 

 sues of the 

 host upon 

 which it has 

 fastened. In 

 the centre of 



this fascicle of hairs some of the elements are tracheid-like 

 cells, which are in contact with ducts. 



352. The roots of many plants have distinctive colors : in 

 some the color belongs to the wood (see 402) ; in others it is 

 due to the cell-sap ; in others, for .instance, the common carrot, 

 to orange-colored crystalline bodies. The crystalline forms 

 found in the parenchyma of the roots of the carrot are minute 

 rhombs, or sometimes rectangular plates to which starch-gran- 

 ules are attached. They are associated with small quantities 

 of protoplasmic matter. (See Chapter IV., for an account of 

 somewhat similar bodies occurring in flowers and fruits.) 



353. The roots of the higher Cryptogams (such as Ferns and 



1 An exhaustive paper on this subject will be found in Pringsheim's Jahrb., 

 1867 : Ueber den Ban und die Entwicklung der Ernahrungsorgaue parasitischer 

 Phaneroganien, von Hermann Grafen zu Solms-Laubach. Koch's paper is in 

 Hanstein's botan. Abhandlunjren, vol. ii., 1875. 



FIG. 9. Vertical section of an hanatorinm of Cnscuta perforating the host-plant. 

 ft, g, absorbing hairs : the central cells are thickened at the base, where they are in contact 

 with the ducts. (Koch.) 



