123 



the non~sse of their material. For esfnmpie, in many gall-forcK:- 

 tions, extensive tissue excrescences are produced, into which 

 .astoni^ing quantities of food stuff a wander, without the exis- 

 tence of any previous injury to the plant hody, even the ve;ry 

 slightest one, which could have led to an abnormal accumulation 

 of material. We must assume that, in cases of this kind, the 

 production of definite currents of food stuffs in abnormal di- 

 rections vrhioh are surprisingly large arises from the action of 

 stimuli, noticeable in the infected cell of the host plant after 

 infection by parasites and under the influence of some unknom 

 poison given out by thera. 



Among vegetative hyperplasias a number of well-differentia- 

 ted groups may also be distinguished according to their etiology . 

 Many are produced by chemical stimulation, others arise after in- 

 jury, etc. In many the proliferation of the tissue may b-e traced 

 back to the clogging of normal currents of food stuffs, in others 

 to an abnormal bringing in of food, resulting from a local non- 

 use of building materials.* In still others, we must assume the 

 existence of special stimuli, which bring about an abnormal sup- 

 ply of food, thus making possible hyperplastic tissue-formatiOBS. 



When considering etiological conditions, we generally fln4 

 ourselves in a more favorable position than do human patholo- 

 gists, to whom the cause of niftny nev/ forrae-tions of tissue is 

 still unknown, 



The abnormal tissues even show a diversity among themselves 

 which is not foiind in any of the chief groups previously dis- 

 cussed. The outer forms of the excrescences, as well as their 

 life history and their histolog y offer a profusion of net eworthy 

 differences, the study of which will be our task. 



T 



(134) It wail suffice first of all to sketch hastily the most im- 

 portant points of view. 



Abnormal nev/ formations of tissue deform the plant organs 

 either as localized, more or less sharply defined excrescences, 

 as diversely formed protuberances, as loosely attached "gall 

 apples", etc, or they change a y/hole organ in such a way during 

 the formation of the abnormal swelling, that the organ itself is 

 at the same time completely consumed and thus, morphologically 

 as well as physiologically, completely gives up its peculiar 

 character. Figures 54 and 55 demonstrate this for a few galls. 

 In the piece of an elm branch shown in the first figure, the leaf 

 at the left hag been caused to form an enormous, pale green pouch 

 by Schizoneura lanuginosq.. b ut has not been taken up as a whole. 

 The form of the leaf has been kept pretty v/ell and a large part 

 of it has not lost the possibility of performing its functions. 

 The same holds ghM in' the galls shown in figure 58 and in many 

 others. 



Figure 55 illustrates two different Cynipides galls, in 

 which buds of the oak have assumed a striking conical f oxm ( Cynip s 

 polyoe ra) or have been grown out into long spindle -like struc- 

 tures, '^C;2SiE§.,£Si2^'' • ^^^ infected organs have thus lost their 

 normal form and function. 



While, in the cases shown in figures 54 and 56 and in numer- 

 ous others, the new tissue formation assumes a definite, usually 

 very elastic form and definite size pr o portions are regularly re- 

 peated in the same kind of galls, there are still other hyper- 

 plaisias, intshe development of which - speaking figuratively - 

 nothing Of this morphologic striving towards a goal can be rec^ 

 ognlzed,*- hyperplasias in which all specific formal character is 



