GALLS 



391 



thorns. Branches of Vaccinmm vitis-idcBa are enlarged by Calyptospora 

 Goeppertiana and those of Juniperus and Chanicecyparis by rusts of the 

 genus Gymnosporangiiim. Various species of the genus Exobasidium 

 produce soft, edible galls. All such galls are mycocecidia (Fig. 84). 



Various algae, such as Cystoseira opuntioides, C. ericoides, and Ecto- 

 carpus Valiantei, live parasitically and cause tissue excrescences, while 

 the higher plants, especially of the family Loranthace^, produce large 

 galls and the so-called wood roses on their host plants. These wood 

 roses are formed by the woody tissues of the host forming a ridge-like 

 growth about the clasping part of the parasite. 



The animal-produced galls known as 

 zoocecidia are some of them of cattiplastic 

 nature and are caused by nematode worms, 

 insects and mites. The most important 

 nematode worm responsible for the forma- 

 tion of galls is Heterodera radicicola, which 

 attacks many cultivated plants both in the 

 greenhouse and in the open. The mite 

 galls include the fleshy (hyperplastic) curl- 

 ings of the leaf edges, shoot tips of various 

 woody plants. Erineum galls, consisting of 

 multicellular cones and ridges, are to be 

 placed here. Dipterous insects produce 

 galls with a prosoplasmatic structure, while 

 the cataplasms produced by them have the 

 form of fleshy curlings of the edges of the 

 leaves of the host plants. Galls are produced Fig. 158. — Crown gall on 



also by the attack of bugs, aphids, or plant raspberry. {After Conn, a gri- 

 1 ,, , cultural Bacteriology, -p. ^06.) 



lice, leaf wasps and gall wasps. They are 



found on roots, stems, leaves, inflorescences and fruits. Such are 



those on the roots of the grape due to Phylloxera vastatrix, etc. 



Histology of Cataplasms. — Usually aside from the slight tissue 

 differentiation cataplasms are composed of abnormally large cells with 

 an abundant protoplasmic content and sometimes with red cell sap, 

 also a large starch content. The primary and secondary tissues are 

 both involved in the formation of the galls. 



Primary Tissues. — ^Leaves, which are infected by fungi on which are 

 formed mycocecidia, show an arrestment of the tissue differentiation. 



