THE ROOT 29 



begonias readily form roots when placed under suitable 

 conditions, and are commonly propagated in this way. 



Some plants grow as parasites upon other kinds of 

 plants ; they thrust their roots into the stems of their 

 hosts, and live by robbing them of sap, thus weakening 

 and often killing the plants on which they grow. 

 Examples of parasitic plants are the strange, thread-like 

 yellow dodders (Cuscuta), often found injuring clover and 

 flax, and the mistletoe common in many parts of Britain 

 on apple and other trees. The method by which this 

 plant spreads from tree to tree is interesting (see chapter 

 on Fruits). 



The roots of these parasitic plants have no .root-caps 

 and no root-hairs, these structures being unnecessary 

 under the peculiar conditions in which these roots grow. 

 The dodder is at times a troublesome pest on clover, but, 

 as a rule, parasitic plants are not serious enemies to the 

 farmer in temperate climates, although they often are so 

 to the tropical cultivator of cocoa, oranges, etc. 



PRACTICAL WORK 



Dig up several germinating seeds and young seed- 

 lings, and examine their roots. Good examples may be 

 obtained by sowing beans, peas, barley, wheat, etc., at 

 intervals of a day in a box of moist sawdust or sand. 

 Water the seeds as required. In warm weather they 

 will be ready in about a week. In the winter a few days 

 longer will be required. Observe that plants with two 

 seed-leaves put out a main, or primary root, which soon 

 forms numerous branches ; on the other hand, plants 

 with only one seed-leaf show no main root, but a number 



