52 



INTRODUCTION TO BOTANY 



saprophytes have fungi growing upon their roots in such ways 

 as to assist in securing food. These are called symbiotic sapro- 

 phytes. The Indian pipe {Monotropa) often has these root 

 fungi (mycorrhiza). 



Partial saprophytes, among flowering plants, are not easily 

 recognized by their form and color, but may be known by their 

 inability to flourish without considerable humus in the soil. 



52. Parasites. The dodders are the most familiar flower- 

 ing parasites. One of the commonest species is abundant 



in the central and north- 

 eastern states, its thread- 

 like, golden-yellow stems 

 forming great tangled 

 masses on many kinds of 

 plants, as clover, golden- 

 rods, and willows, that 

 grow in damp places. 

 The dodders (fig. 34) and 

 some root parasites, such 

 as the beechdrops, squaw- 

 root, and cancer-root, are 

 complete parasites and have 

 no green foliage. Other 

 plants, such as the mistle- 

 toe (fig. 35), have green leaves and do photosyniJaetic-work, 

 but depend on the host for water and the mineral substances 

 dissolved in it. Such plants are called partial parasites. 



53. Damage inflicted by parasites. Many parasites take so 

 much water and plant food from the host that they may 

 cause serious injury to cultivated plants and to forest trees. 

 The flax dodder and the clover dodder often do great damage 

 to crops in this country and in Europe, and another species * 

 is sometimes troublesome in fields of alfalfa. In the south- 

 western states the American mistletoe is so injurious to dicoty- 

 ledonous trees that it is often necessary to cut it away from 



1 Cuscuta arvensis. 



FIG. 35. Mistletoe growing upon a branch 



of an apple tree 

 After Bonnier and Sablon 



