128 



to the conditions under v/Mch they are produced has not been 

 answered satisfactorily and would repay experimentation. Sim- 

 ilar formations of ridges are already knoivn in other plants; 

 in the case of more vigorous development, they furnish a trans- 

 ition up to a duplication of the blade, 



Hottas^ produced experimentally on the roots of Vic la FabR , 

 similar formations of lesser extent and simpler composition. If 

 these roots were put in plaster casts, so that only little holes 

 here and there above the tip made possible any further disten- 

 sion; these holes were filled by "correlative" growth in thick- 

 ness of the roots. The form of the homooplastic excrescenees 

 corresponded to the form of the space at its disposal. It Is 

 possible in cases of this kind to speak of correlation-homoo- 

 plasia, (see below). 



Because of their external similarity to those above men- 

 tioned, the peculiar ©bnormal tissue excrescences may be men- 

 tioned here, v>?hich Hameo observed on the roots of Oardamine 

 amaru. They are produced exogenously and are connected with 

 the central bundle of the mother-organ by a procambial cord, 

 v/ithout, according to Wemec, its leading in them to the forma- 

 tion of a true vascular bundle. Sometimes they bear root-hairs. 

 Similar pathological structures occur also on the roots of 

 Roripa, The conditions, with the fiilfillment of which their 

 formation is connected, are not yet known exactly. 



II. The homooplasias named in the following are character- 

 ized by the fact tha.t only single tissue f oar ms of an organ are 

 super-abundantly developed and no production of local excrescen - 

 fl41) ces . by which means the histology of the organ is altered. In- 

 leed eaol) tissue form can, under certain circumstances, under- 

 go a homooplastic formation, 



1. A group well characterissed physiologically is shown in 

 those forms, in which the abnormally abundant formation of tissue 

 is caused by some increased demand made upon it. Tissue forma- 

 tions of this kind which we will term work . or activity homoo - 

 plasias . (or hyperplasias), have long been known to physicians. 

 Muscles of which more and more is required become enlarged, ap- 

 parently by increase of their elements; as are also blood ves- 

 sels upon which especially strong strain is put, after stoppage 

 of other blood vessels, and the like. 



We must make investigation^ to learn if plants are also 

 capable of forming a ctivity-horaooplasias, 



^ Rudow (Einige Missbildungen as Pfl. herborgerufen durch 

 Insekten, Ztschr. f. Pfl.-Krankh. , 1891, Bd. 1, p. 532) thought^ 

 mistakenly that ho had recognized a mite gall in the Aristolochia 

 • ridges. Literature on these and similar structures is to be 

 found cited in Sorauer, Handb. d. Pf lanzenkrankh. . 2. Aufl., Bd. 

 1, p. 239. Investigations made by Magnus (Sitzungsber. Prov. 

 Brandenburg, 1877, Bd. XIX) show that with tissue excrescences 

 mav be united also phenomena of arrestment in the ad;5acent parts 

 of" leaves (Arrestment in the development in size of single meso- 

 phyll cells, scanty development of chlorophyll, and the like). 

 In the cases which I investigated, the latter were always missing- 



2 Ueb. d. Einfl. v. Druckwirkungen auf d. Wurzel von Vicia 

 ffaba. Dissertation Bonn. 1901. 



^ Ueber schuppenformige Bil^ungen an d, Wuraeln v. Oarda- 

 mine amara, Sitzungsber, Kgl. bohnj^ Ses. Wise,^ 1901, K. VI. 



