I20 
MORPHOLOGY 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 which contain tannin ; the true laticiferous vessels of Cicho- 
riacese, Campanulaceae, 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 Ipomcea, Argemone, Gomphocarpus, 
Euphorbia, Carica, Lactuca, and in Campanulaceae (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 Pith, 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. 
