TISSUE-SYSTEMS 71 



liminary review of the various kinds of tissues and organs, it is necessary 

 to define the conception of an anatomico-physiological system. This 

 term is employed, in the present work, to designate the totality of 

 the tissues and mechanisms engaged in the performance of a 

 particular physiological function. The number of structures comprised 

 in a given system will, of course, vary with the complexity of the 

 function concerned and with the extent to which the latter is subdivided 

 into partial functions. The great majority of anatomico-physiologieal 

 systems are also tissue-systems, that is to say, they are mainly or 

 entirely composed of actual tissues. That this is not necessarily the 

 case is shown, for instance, by a consideration of the ventilating system, 

 which is largely composed of intercellular air-spaces : the secretory and 

 excretory system, again, can only be regarded as a tissue-system in a 

 metaphorical sense. 



PRELIMINARY REVIEW OF THE VARIOUS ANATOMICO-PHYSIOLOGICAL 



SYSTEMS. 



I. Meristematic tissues (primordial meristem ; primary and secondary 



meristems). 

 II. The tegumentary or dermal system (epidermis, cork, bark). 



III. The mechanical system (bast-fibres, wood-fibres [libriform cells]; 



collenchyma ; sclerenchyma). 



IV. The absorbing system (absorbing tissues of terrestrial roots, 



especially root-hairs; rhizoids; the velamina of aerial roots ; 

 water-absorbing trichomes of leaves : haustorial absorbing 

 tissues of embryos and parasites). 

 V. The photosynthetic system (palisade-cells and spongy parenchyma; 

 chlorophyll- containing parenchyma generally). 



VI. The conducting system ("conducting parenchyma," including 

 xylem-parenchyma, the parenchymatous elements of the pith, 

 cortex and medullary rays, and the parenchymatous bundle- 

 sheaths [border parenchyma] ; vascular bundles, comprising 

 hadrome and leptome ; latex-tubes). 

 VII. The storage system (water-tissues: storage-tissues of seeds, 

 tubers and bulbs). 

 VIII. The ventilating system (the intercellular air-spaces together 

 with their external openings or pneumathodes, especially 

 the stomata and lenticels). 



IX. Secretory organs and excretory reservoirs (hydathodes, nectaries, 

 digestive glands : mucilage-, oil-, and resin-glands : mucilage-, 

 oil-, resin-, and gum-passages : raphide-sacs, etc). 

 X. Motor tissues (riying-hairs and -tissues ; floating-tissues : hygro- 

 scopic and other non- vital motor tissues : vital motor tissues). 



C 



