116 



MINUTE STRUCTURE OF THE ROOT. 



Sol. Parasitic roots,-' or those which fasten themselves for 

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

 iar conditions under which the}- live, that the}- require special 

 mention. Their structure can be best understood bj- a section 

 througli the root of Cuscuta. 



Here there is no centi-al cylinder, properly so called, nor is 

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



as reduced 

 to a pilifer- 

 ous la^-er, 

 since some 

 of its cells 

 i^ are pro- 

 \ longed to 

 form a fasci- 

 cle of long 

 hairs in inti- 

 mate .contact 

 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-lilfc 

 cells, whicli are in contact with ducts. 



352. The roots of manj- 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 crj-stalline forms 

 found in the parenchj-ma 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 liigher Cryptogams (such as Ferns and 



1 An exhaustive paper on this subject will he found in Pringsheim's Jahrh., 

 1867 : Ueber den Ban und die Entwicldung der Eniahrungsorgane parasitischer 

 Phanerogam en, von Hermann Grafen zu Solms-Laubach. Koch'is paper is in 

 Haustein's botan. Abhandlungen, vol. ii., 187.5. 



Fig. 98. Vertical section of an haustorlum of Cuscuta perforating the host-plant. 

 17, g, absorbing hairs ; t he central cells are tliicl^ened at the base, where they are in contact 

 with the ducts. (Koch.) 



