in 



main far below these in number. Heteroplastic gall foiroations 

 occur ^in very different kinds of plants, appear on all plant 

 organs and may be traced developmentally to very different 

 normal tissue -^forms, A few general notes might" be in order 

 before we proceed to a description of the different fall forms, 



(190) One generally terms galls, or Cocidia''-, those variations 

 in form which are caused by foreign organisms. Thomas, whose 

 definition of the conoention of the gall has received the loost 

 approval, explr.ins as a gall, "every variation in the form of 

 plants which i« caused by a parasite**, 'and adds*, "in this ex- 

 planation the word formr'.tion is to be taken directly in the 

 sense of the process (therefore active), not merely in the 

 sense of its result. Each leaf eaten or mimed by caterpillars 

 shows a formal variation. Ho one will associate such changes 

 with cecldia. To the nature of these latter belongs active 

 participation of the plant, its regotion against the e^ttf'liltiB 

 then experienced"**. 



I have attempted at an e@rller opportunity^ to define 

 more sharply the definition given by Thomas and have advised 

 a closer consideration of the biological connection between 

 the plant bearing the goll and the foreign organism producing 

 it, in the formulation of the definition. Clearly there are a 

 number of variations of form which are caused by stimuli given 

 by the foreign organism and in which abnormal tissues are pro- 

 duced, without one's venturing to call them galls. Such a 

 case is met with perhaps when a"mining path" is filled with 

 callus (examples above p. 163), Wo one will contend that such 

 oases present gall -format ions. The abnormal tissues show no 

 connection with the foreign organism,- aside from an etiologi- 

 cal one , In our opinion one essential of a gall is that the 

 abnormal psrts of the JJlant affected bring about symbiotic re- 

 lationship between these and the parasites producing the gall. 

 These symbiotic relations are primarily of a nutritive physio- 

 logical nature; the abnormal tissues furnish food for the par- 

 arsites. Additional relations exist since the host plant not 

 only furnishes sufficient maintenance, b\it also as good shel- 

 ter. The gallB are thus formal variations of the plant which 

 promote the development of the parasites and are in this sense 

 "expedient" for them. Now, since according to ^he above sym- 

 biosis with the producer of the gall always signifies a loss 

 of nutritive material for the host organism, the part which 

 bears the gall often dies a premature death and further, since 

 in all cases as yet known the parasite prodixcing the gall per- 

 forms in return no service to the host, as one is often in- 

 clined to assume in So-called mutualistic symbiosis, we are con- 

 cerned in cecldia with formal variations v/hich are injurious 

 to the development of the organism bearing the gall. 



Of all the variations in form satisfying the demands of our 

 definition, we will naturally treat in the following only those 

 in w*\ich abnormal tissues are produced. To present the doubling 



^ Thomas, (^ur Kenntnis der Milbengallen und Gallmilben eljc, 

 Zeitsch. f. ges. Uaturw., 1873, Bd. XLII, p. 513) has introduce^ 

 this word (derived from Knxls), Compare also the critical re^ 

 marks by Trotter, Studl oecidiologioi II (Huovo giorn, hot, 

 ital., 1901 W. S. Vol, VIII, p. 557). 



^ Loc. cit. p, 513, 514. 



^ Kuster, Ueber einige wichtige Fragen der pathol. ?flan- 

 ssenanat- Bloloer. Oentrabl.. 1900 "Rfl. mc. n. R29. 



