102 MORPHOLOGY OF TISSUES. 



All that has hitherto been said concerns only the elongated elements of the fibro- 

 vascular bundle ; the radially extended elements (xylem- and phloem-rays) are a pecu- 

 liarity of the open fibro-vascular bundles of Dicotyledons and Conifers. 



Sect. 17. The Fundamental Tissue (Grundgewebe). — By this name I de- 

 signate 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. 

 The fundamental tissue consists very commonly of thin-walled succulent paren- 

 chyma filled with assimilated food- materials ; but not unfrequently it is thick- 

 walled ; sometimes separate portions assume the form of string-like tissues which 

 consist of sclerenchymatous strongly lignified prosenchyma cells. The most 

 various forms of cells and tissues may arise in the fundamental tissue as in the 

 epidermal system and the fibro-vascular bundles ; a portion of the fundamental 

 tissue itself may persist from the commencement in a condition capable of divi- 

 sion, while the surrounding portion passes over into permanent tissue ; or special 

 layers of the fundamental tissue, long after it has been transformed into perma- 

 nent tissue, may again become subject to cell-division, and a generating tissue thus 

 be produced, out of which originate, not only new fundamental tissue, but also 

 fibro-vascular bundles {e.g. in Aloineae). 



In Thallophytes and many Muscineae the whole mass of tissue, with the 

 exception of the outermost layer, which is often developed as epidermal tissue, may 

 be considered as fundamental tissue ; but in these cases, in consequence of the ab- 

 sence of the fibro-vascular bundles, this distinction has but little practical value. In 

 Mosses with string-like formations in the stem it may appear doubtful whether these 

 are to be considered as peculiar forms of the fundamental tissue or as very rudimen- 

 tary fibro-vascular bundles. In Vascular plants, on the other hand, the independence 

 and pecuHarity of the fundamental tissue, in contradistinction to the epidermal system 

 and the fibro-vascular bundles, is at once apparent ; it here fills up the interstices 

 of the fibro-vascular bundles within the space enclosed by the epidermal tissues. 

 Where the fibro-vascular bundles are closed and show no increase in thickness 

 (as in many Ferns), the tissue is frequently the most largely developed; where, 

 on the other hand, closely crowded fibro-vascular bundles, by the development of 

 cambium, produce in succession large masses of layers of wood and phloem (as in 

 stems and roots of m.any Conifers and Dicotyledons), the fundamental tissue becomes 

 a constantly less important portion of the whole organ. The disposition of the fibro- 

 vascular bundles in stems is commonly of such a nature that the fundamental 

 tissue is separated into an inner pith-portion, surrounded by the bundles, and an 

 outer cortical layer enveloping the bundles. Since the bundles are not in contact 

 laterally, or only partially so, there still remain between them portions of the fun- 

 damental tissue which connect the pith with the cortex, and are 'termed Medullary 

 Rays. If the fibro-vascular masses of an organ form an axial solid cyHnder, as occurs 

 in some stems and in roots, the fundamental tissue is developed only as cortex. 



(a) Critical. The whole course of my description of the tissue-system requires the 

 introduction of the idea of a ' Fundamental Tissue.' It has, in fact, long been required, 

 since it was often necessary, in anatomical descriptions of the collective masses of the 

 tissue which are neither epidermal nor fibro-vascular bundles, to distinguish them by 

 some common term. Many writers employ the term Parenchyma in this sense in oppo- 

 sition to the fibro-vascular bundles and the epidermis ; but this usage is not scientific ; 



