34 CLASSIFICATION OF CELL TYPES, TISSUES, AND TISSUE SYSTEMS 



(1875, pp. 77-78), of three principal Sij.sicms of Tissues, viz.: 

 (1) the Epidermal ISystem, under Avliicli are grouped the epi- 

 dermal and cork laj'ers; (2) the Fascicular System, Avhich con- 

 sists of the variously-arranged xylem and phloem; and (3) the 

 Funclamental Tissue System, which Sachs defined as "those 

 masses of tissue of a plant or of an organ which still remain after 

 the formation and development of the epidermal tissue and the 

 fibro-vascular bundles." Sachs (op. cit., p. 103) emphasized that 

 his classification was not concerned basically with the forms of 

 cells "but with the contrast of different systems of tissue, each 

 of which may contain the most various cell-forms." It is lastly 

 of interest to note that Sachs did not attempt to demarcate 

 rigidly "permanent" and "meristenuitic" tissue but on the 

 contrary emphasized the ability, especially of the epidermal and 

 fundamental systems, to regress to the state of a " formative ' ' or 

 dividing tissue. 



Sachs' classification of the adult vegetative tissues of higher 

 plants into three main groups is appealing in its apparent sim- 

 plicity and practicability. That it does indeed possess consider- 

 able pedagogical value is shown by its adoption (with or without 

 minor changes) in such modern texts as Sinnott (1935) and 

 Molisch (1[)36). From a more technical standpoint, Sachs' classi- 

 fication is also used by Jeffrey (1917, pp. 8-13), who emphasizes, 

 however, that the structural boundaries between the three tissue 

 systems are more evident in lower than in higher vascular plants. 

 Furthermore, the limits of the systems appear less sharply defined 

 in tlic siciii than in the "more conservative" leaf and root. In 

 organs whei-e secondary growtli is jU'ominent, the boundaries 

 betAveen the vascular and fundamental systems may disappear 

 and "in such cases the limits of the tissues can only be inferred 

 from comparative and developmental anatomy." The chief 

 objection which has been repeatedly raised against Sachs' classi- 

 fication is concerned with the indefinite physiological as well as 

 .structural characterstics of the "Fundamental Tissue System." 

 In some organs, this system may consist largely of parenchyma, 

 but many other cell tyi>es or tissues may be present. The funda- 

 mental tissue system, as Ilabei-landt (1914. p. 712) states, in- 

 cludes "green photosynthetic parenchyma, colorless water-tissue, 



