SYSTEMS OP TISSUE CLASSIFICATION 35 



storage-parenchyma, meehaiiieal strands and cell-masses, endo- 

 dermal layers, and the mnltifarions tissues which make up peri- 

 carps and seed coats. No one, therefore, will venture to maintain 

 that "ground-tissue" constitutes a "whole of definite physio- 

 logical character." 



2. Haherlandt's classification. Probably no scheme for classi- 

 fying plant tissues has been carried out so consistently from a 

 single point of view or in such detail as Ilaberlandt's "Ana- 

 tomico-Physiological Classification." According to Ilaberlandt's 

 viewpoint, the "principal function" should be the sole guide in 

 the designation of any specific tissue "system." The "principal 

 function" of a tissue is defined as "that form of physiological 

 activity with which its most obvious and important anatomical 

 features are correlated." The application of this idea resulted 

 in the distinction by Haberlandt (1914, pp. 71-72) of twelve 

 "anatomico-physiological tissue systems," each of which is typi- 

 fied by one major or "principal" function: e.g., absorption, con- 

 duction, protection, support, etc. With reference to the merits 

 of his scheme of classification, he contends that "the anatomico- 

 physiological definition and arrangement of tissues provides the 

 broadest and most natural of all systems of tissue classification, 

 since from this point of view the plant-body is regarded not 

 merely as a more or less complex aggregate of formal elements, 

 but also as a living organism, composed of a number of functional 

 units and engaged in a corresponding number of physiological 

 activities, whch all contribute to the safety and welfare of the 

 whole." 



Haherlandt's high estimate of the value of his method for 

 classifying tissues has been amply justified by its wide adoption 

 in elementary as w^ell as more advanced treatises on plant his- 

 tology. Tsehirch (1889) and Palladin (1914), for example, 

 follow Ilaberlandt's system with little modification and Molisch 

 (1936) champions its merits for the advanced student. In this 

 country, the anatomico-physiological classification has likewise 

 proved popular and is utilized, in a somewhat simplified form, 

 in such a recent compendium as Hayward (1938). But one of 

 the most significant illustrations of the prestige and influence of 

 Haherlandt's ideas and classification is furnished by the ambi- 



