Abnormal Growth 283 



and Digitalis purpurea. Pelory is frequent in Labiatae, where it usually 

 occurs at the top of the inflorescence. 



As to the cause of pelory, opinion is divided. In cases such as Digitalis 

 the difference between the bilabiate and the radial condition is clearly 

 induced by gravity for it can be reversed experimentally. Peyritsch found 

 that in Labiatae it may be induced by strong illumination. Sachs believed 

 that physiological factors are operative in causing it. There are many 

 cases, however, reported by Vrolik, Darwin, de Vries, Baur, Lotsy, and 

 others, where this type of abnormality, or at least a tendency to produce 

 it, is inherited. 



Fig. 11-5. Peloric flower of Linaria 

 vulgaris, almost radially symmetrical. 

 (From Goebel.) 



PRODUCTION OF NEW TYPES OF ORGANIZED STRUCTURES 



In organoid galls and similar types of abnormalities that have been dis- 

 cussed, structures recognizable as those found in normal plants are 

 present, though their size, form, and arrangement may be altered and the 

 general pattern of organization distorted. In the group now to be consid- 

 ered the structures produced are entirely novel and cannot be placed in 

 any such morphological category as leaves or stems. They can hardly be 

 regarded as organs, but they are much more than tissue abnormalities 

 for they have a constant and specific form, size, and structure and a very 

 considerable amount of histological differentiation. They result from the 

 attack of parasites. In most cases they undergo a definite period of devel- 

 opment, or life cycle, correlated with that of the parasite and thus are 

 different from the cataplasmatic abnormalities to be discussed later. In 

 Kiister's terminology they are prosoplasmatic galls. There is no sharp line 

 between these and the simpler gall types but their large number and 

 definite forms set them apart as a rather distinct group. The majority are 

 zoocecidia (galls formed by animals). The most conspicuous and best 

 known owe their origin to parasitism by the gall wasps or cynipids, a 

 family of the Hymenoptera. Others are produced by flies of the gall 

 midges and simpler ones by mites. A few are the result of fungus parasites. 



