27 



22 



* 



limited field of action may in places arrest growth in thick- 

 ness, ^uch as strong pressure (Kuster, loc . cit.) disturban- 

 ces in nutrition due to parasites, etc .1 



In conclusion, still a reference to dwarf forms, the 

 anatomy of which Gaucher (loc. cit.) has described in detail. 

 According to liis observations, the scanty development of the 

 secondary tissues or their complete absence may be added to 

 the constant histological characteristics of dwarf forms. 

 In many cases no meristematic zone whatever is demonstrable 

 between :'cylem and phloem, in others a cambium appears, which 

 develops, however, only a moderate activity. Figure 6 makes 

 very clear the difference between a .normal stem (a) and a 

 dwarfed one (B) of Erigeron canadensis. Between the two ex- 

 tremes here shown, all transitOBal forms with more or less 

 well developed secondary tissues are possible. 



As a matter of course, in the present discussion, only 

 a limited number of e::amples is given, which might easily'' have 

 been increased. A continuation of their entimeration would 

 give, ho?;ever, no new points of view, and may well be aban- 

 doned. For the rest, the literature quoted in the succeed- 

 ing divisions cites numerous other examples of hypoplastic 

 decrease of the cell number, 



B. SIZE 0? THE CELLS 



As may be supposed from the very beginning, abnormally 

 small cells,- when considered ontogenetically may be produced 



in different ways : 



They may divide anew, before they have reached the 

 size which the cells under normal conditions usually have 

 when ready to divide. No law exists which v;ould bring cell 

 division into compulsory dependence upon a definite cell- 

 size. This method of production plays an especial part in 

 the case of lower organisms which increase by division. Or 

 the growth in length following the last cell division, is 

 either omitted or ends prematurely; or the cells end the 

 course of their development prematurely, so that all the 

 processes of growth and division are lacking, which under 

 normal development would still have taken place in then. 



In the following description it will prove advisable 

 not to take as a basis developmental differences in the dis- 

 tribution of materials, but to describe in order the phen- 

 omena of arrestment in different organisms and kinds of tis- 

 sue. We will begin therefore, with an example of the first- 

 named mode of development. 



!• Brunchorst, Wogle norske shovsygdomme , Bergens 

 Mus, Aarbog. 1892.- Just, Jahresbericht, Bd, SSIa, p. 438, 

 (einseitige nach Infektion met Peridermium Pini), Mer, Le 

 chaudron du sapin. Rev. gen. de Bot^, 1894, T, VI, p, 153, 



