I20 MORPHOLOGV OF TISSUES. 



will have been seen from Sect. 14; and this happens especially in the phloem. Thus 

 lithocysts, cells containing pigments, receptacles for oil, and other idioblasts like the 

 rows of cells in Phaseolus M'hich contain tannin; the true laticiferous vessels of/]icho- 

 riaceae, Gampanulacese, and Lobeliaceae, belong to the phloem, while those of Papa- 

 yaceae and Aroideae belong to the whole fibro-vascular bundle. In may even occur 

 that vessels belonging to the xylem contain latex, as in Ipomceaj Jrgemone, Gomphocarpus, 

 Euphorbia, Carica, Lactuca, and in Gampanulaceae (David, /. c). In the same manner 

 it has already been shown, in Sect. 14, that the secretion-canals — i.e. intercellular 

 spaces containing oil, resin, or gum — may occur either in the phloem, or in the 

 xylem, or in both. 



Sect. 17. The Fundamental Tissue. — By this name I designate the tissue 

 of a plant or of an organ which still remains after the formation and development 

 of the epidermal tissue and the fibro-vascular bundles. It consists very com- 

 monly of thin-walled succulent parenchyma filled with assimilated food-materials ; 

 but not unfrequently it is thick-walled ; sometimes portions assume the form of 

 strings of strongly lignified prosenchymatous cells. The most various forms of 

 cells may arise in the fundamental tissue, as in the epidermal system and the fibro- 

 vascular bundles; a portion may persist in a condition capable of division, while 

 the surrounding portion passes over into permanent tissue ; or special layers of 

 the fundamental tissue, long after it has been transformed into permanent tissue, 

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

 duced, 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; but in these cases, in consequence of the 

 absence of fibro-vascular bundles, this distinction has but little practical value. 

 In Mosses, which have string-like cell-groups in the stem, it may appear doubtful 

 whether these are to be considered as peculiar forms of fundamental tissue, or 

 as very rudimentary fibro-vascular bundles. In Vascular plants, on the other hand, 

 the independence of the fundamental tissue, in contradistinction to the epidermal 

 system and fibro-vascular bundles, is at once apparent; it 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 do not increase in thickness 

 (as in many Ferns), it is frequently the one which occupies the greatest 

 space; where, on the other hand, closely crowded fibro-vascular bundles produce 

 large masses of xylem and phloem by the development of cambium (as in the 

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

 less important. The fibro-vascular bundles in stems are usually so arranged as 

 to separate the fundamental tissue into an inner medullary portion the Ptlh, sur- 

 rounded by the bundles, and an outer cortical layer or Cortex enveloping them. 

 Since the bundles are not in contact laterally, or only partially so, there still remain 

 between them portions of the fundamental tissue which connect the pith with the 

 cortex, and which are termed Medullary Rays. If the fibro-vascular bundles of 

 an organ form a solid axial cylinder, as occurs in some stems and in all roots, 

 the fundamental tissue takes the form of cortex only. 



