THE FUNDAMENTAL TISSUE. 
123 
loose parenchyma with large intercellular spaces ; this innermost portion of the funda- 
mental tissue is enveloped by a thin-walled tissue without interstices, which is seen 
on longitudinal section to be prosenchymatous ; the cells are pointed at both ends, 
and penetrate to a considerable distance between one another ; towards the circum- 
ference they become gradually narrower and more pointed ; the outermost are dark- 
walled, and form the epidermal system which gradually passes over into this fundamental 
tissue. In Lycopodium Chamcecy parts sus (B) the axial cylinder, which consists of several 
fibro-vascular bundles, is surrounded by a thick layer of greatly thickened prosenchyma ; 
in the young stem the cells are similar to those of Selaginella ; but here also the 
prosenchymatous cells of the fundamental tissue undergo an enormous thickening. This 
prosenchymatous fundamental tissue is in its turn enveloped by a layer of tissue, the cells 
of which are thin-walled and not prosenchymatous ; this layer is a descending continua- 
tion of the fundamental tissue of the leaves, which envelopes the stem everywhere, 
and is itself covered ^y a clearly developed epidermis. 
(c) The Forms of Cells and Tissues in the system of the fundamental tissue have not 
yet undergone a comparative and comprehensive investigation \ like those of the fibro- 
vascular bundles. Out of the very 
scattered material I select the fol- 
lowing for the information of the 
student. 
Irrespectively of many altogether 
special phenomena, it is chiefly in 
connexion with the true epidermal 
tissue on the one hand and the fibro- 
vascular bundles on the other hand 
that the differentiation of the funda- 
mental tissue has to be considered. 
Certain forms of this tissue occur as 
strengthenings, or at least as accom- 
paniments of the epidermal tissue, 
and have already been described as 
Hypoderma; other masses of tissue 
accompany the separate fibro-vascular bundles as partially or entirely closed envelopes or 
sheaths; these I term generally Bundle-sheaths or Vascular Bundle- sheaths. In the 
same manner the whole remaining internal space of the organ concerned is commonly 
filled up by other forms of tissue, which do not, as for the most part the two former 
do, occur in the form, of layers, but in masses ; these I will designate simple Inter- 
mediate Tissue. Each of these combinations may be composed of very diflferent forms 
of tissue. 
(a) The Hypoderma appears sometimes as a thin-walled succulent watery tissue, 
as in the leaves of Tradescantia and Bromeliaceae ; in the stems and petioles of Dicotyle- 
dons it commonly consists of collenchyma, the cells of which are extended longitudinally, 
narrow, and thickened in the angles by a mass capable of great swelling ; or the 
hypodermal fundamental tissue is developed in a sclerenchymatous manner, as in the 
stem of Pteris aquilina ; or it occurs in the form of thick-walled but flexible fibres, 
forming either layers and bundles as in the stem of Equisetaceaj and leaves of Goniferas 
(Fig. 102), or in long isolated fibres, similar to true bast-fibres, e.g. leaves of Cycadeae. 
In all these cases the hypodermal cells are extended longitudinally; but when layers 
capable of great resistance are also required, the cells often extend in a direction 
vertical to the surface of the organ, and, increasing greatly in thickness, form layers of 
^ Since the publication of the 3rd edition of this work, a close investigation of the fundamental 
tissue has been undertaken by Russow (Z. c.) ; he has however occupied himself chiefly with the 
various forms of the bundle-sheaths or ' Critenchyma.' 
Fig. ioi.— Transverse section tlirough the undergroinul slcin of 
Pteris aqitili7ia; h root-hairs; beneath the epidermis are strongly thick- 
ened brown-walled cells ; q one lying deeper and less strongly thickened ; 
a part of the wall is seen in front ; se cells of the deeper layers containing 
starch, forming the passage to the inner colourless parenchyma of the 
fundamental tissue. 
