92 SCIEXCE PROGRESS. 



stituted by A. Mann at my suggestion, he succeeded 

 partially in effecting a like transformation in Pisum sativum 

 in all these cases the effect was due to definite material 

 causes, and we are justified, therefore, in assuming that a 

 similar cause operates when the malformations are caused 

 by animals or by parasitic moulds. I confine myself to the 

 former, since such causes have received far less attention 

 than those of the latter class. 



The experiments of Peyritsch on the production of 

 double flowers and other- variations of structure by artificial 

 means are of special interest.^ Unfortunately the death of 

 the investigator has rendered it impossible tor him to give 

 the full results of his experiments in detail, and we possess 

 only the short communication referred to along with 

 another ^ in which the author showed that by infecting 

 species of Arabis with species of Aphis, chloranthy may be 

 artificially produced, provided that the development of the 

 buds selected for the operation be not too far advanced. 

 The chloranthy was accompanied by interference with the 

 development of the sexual organs, the pollen in particular 

 being rudimentary, and apparently incapable of performing 

 its function. 



More pronounced malformations were produced by the 

 infection of other plants, e.g., some Valerianacese and 

 Cruciferae, with Phytoptus. These consisted partly 

 of abnormalities in the leaves, and partly in various 

 kinds of double and proliferating flowers. The first group 

 generally consisted in the arrangement of the teeth of the 

 leaves in a comb-like manner on leaf flaps which projected 

 considerably beyond the general outline of the leaf In 

 Centranthus calcitrapa this appearance often took the form 

 which Masters in his Vegetable Teratology (p. 445), de- 

 scribes as " E nation of leaf-organs". 



In the inflorescences of Cruciferae the bracts to the 

 flowers which are usually absent (aborted) in this order 



^ "Sitzungsber. der Kais, Akad. d. Wissensch. in Wien," Bd. xcvii., 

 1888. 



" " Aetiologie der Chloranthien einiger Arabis-arten," Fringsh. /ahrb.. 



