84 MANUAL OF TREE DISEASES 



formed on the surface of the ground. Several kmds of toad- 

 stools and puff-ball fungi have been proved to be mycorhizal 

 fungi. Ectotrophic mycorhizas are recognized by the short, 

 stubby, lateral rootlets, which are covered with the fungus 

 mantle and may be white, brown, yellow or red. The same 

 tree may show several different kinds of mycorhizas, each caused 

 by a different species of fungus. When the mycorhizal pro- 

 duction is profuse, whole clusters of the stubby roots may form 

 a coral-like structure. The endotrophic mycorhizas on maple 

 roots form bead-like swellings, often in chains. The mycelia 

 of some endotrophic mycorhizas have been found to produce 

 fruiting-bodies, which place them in the g'enus Phoma. 



Reference 



McDougall, W. B. On the mycorhizas of forest trees. Amer. Jour. 

 Bot. 1 : 51-74, pis. 4-7, flg. 1. 1914. (BibUography given.) 



Roots Parasitized by Flowering Plants 



Several species of flowering plants attach their root-like 

 organs to the roots of other plants and trees, and draw a certain 

 amount of food materials from them. All degrees of para- 

 sitism are found, from the species of the broom-rape family 

 (Orobanchaceae) which develop no leaves or chlbrophyl and 

 are entirely dependent on other plants for food, to those tj-pes 

 which develop normal green foliage above ground, and some- 

 times grow without forming any attachments to the roots of 

 other plants. Certain species of Comandra have been found 

 to be of the latter type. Their roots normally develop disc- 

 like attachments, which connect the tissues of the Comandra 

 roots with the roots of various other plants. They have been 

 found attached to the roots of the following trees : maple, 

 birch, chestnut, poplar, oak and sumac. Very little damage is 

 done to the tree. Examples of the former type, mentioned 



