256 



each ti^^ ^^^^^ possible kinds of tissue can be produced fTom 

 a dlffifp^^rl4??°''^^''f *^ !^^ present extent of our knowledge, 

 far thnt ?J2 ^-P ^""^^^^ betwenn the chief tissue fonns in so 

 difflo«lV!^i,^''lv''"'^!^ as already stated, reacts with greater 

 lesrnui!L,,o''!^ *5^ J*^r ?°™^ °^ *i^^^^ ^^'^<^ usually fSrnishes 

 derlc???v«2 f Pr«fi°ts during processes of division, while its 

 tlon aft fl^%?;° ^°*^2eein capable of so extensive a differentia^. 

 Yet 1-hof^?J^°^''?,°^ T'T^''^ ^^^"""^^ °^ 0^ vascular bundle tissue^. 

 R«« Jn'^L i® ®®1J:^ °^ *^® epidermis are able to produce all tis~ 

 sntn«+r^. v°™ themselves, has been proved by the r.dventitious 

 wiS^ f I "egonia leaves - to name only one example. 7hese are 

 known to develop from epidermal cells.. 



«*4o+'^^^*'^?°^^ ^'^ plants, no auch"speoifloness of the tissue" 

 n J;^i ^-^ ^^ usual In animal nnd human tissues. Do we find here 

 o* J ^P'^?! ^^ principle betvreen animal and vegetable tissues, 

 or 18 the difference explained perhaps by the fact that the 

 C^^nc^^ P°^^®^„o^^ development of the anlrat^.l tissues is determined chief- 

 ly by "internal" factors and is not so actively influenced by a 

 Change of "external" factors, ?/ith which v;e work in any experi- 

 ment, as is the course of development of vegetable tissue? 



fl^^4^ The knoi7ledge thest similar derivatives can be produced fet ' 

 aiiterent places, i. e, from different parts of the plant body, 

 TJhat therefore^ the capacities of the different plant tissues 

 are fundamentally and everjTWhere the same forces as to the c&n- 

 oluslon that, under normr.l as Ander abnormal conditions, the 

 developmental fate of the cells and tissues in the last in- 

 stance (within the possibilities of the plant) are determined 

 only by the forces acting upon thera, by the quality, intensity ' 

 and combination etc, of these. From this point, we are led at 

 once to new tasks and new discussions. When, in the formr-tion 

 of callus from pith and bark, or of galls from the derivatives 

 of the ground tissue etc, the same vascular bundle elements are 

 produced which usually in a normal course of tissue development 

 occur in a circle around the medullary cjrlinder or among the 

 cell elements furnished from the cambium, the question must be 

 asked,- after v;e have recognized as impossible any specific 

 cell-constitution,- whether, in the cases of normal and abnormal 

 cell production here named, the same formative processes may al- 

 ways ib the last instance be traced to th» action of the same 

 factors. We must ask ourselves the s^me question, 'vvhen the de- 

 rivatives of the ground tissue and of the 'vascular bundle tissue 

 grow out to just such epidermal cells and hairs as the elements 

 of the dermatogen under normal conditions. The treatment of this 

 end all similar questions v/hich might lead to a developmental 

 mechanics of iplant tissues , has never been attempted as yet. It 

 iia s air eady , however , be c bme quite evident that no un surmount sble 

 hinderances stand in the way of carrying out this treatment and 

 many valuable results may be expected from it, I mean to dis- 

 cuss later in another connection the Incentives to a treatment 

 of developmental mechanical problems (here indicated) vrhich the 

 pathologitjQl anatomy of plants and especially the anatomy of 

 galls, can give, 



■^ It should be noted here that the galls, to vrhich we must 

 refer first of all, have been by no means sufficiently investi- 

 gated fribm histological and developmental points of vidv/, Thus, 

 for instance, developmental reports on the abundant gall-flora 

 of JTorth America are practically entirely lacking - the galls of 

 Southern Europe have been investigated, at least predominantly 

 as to their habitats and their most striking morphological p6cul- 

 larities,- Perhaps I will succeed in inciting by these linesr, 

 nev; developmental studies, which, it must be stated, are urgent- 

 ly desired. 



