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 Chamcpcyparissus (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 by 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 different forms 

 of tissue. 



(a) The Hypoderma appears sometimes as a thin-walled succulent watery tissue, 

 as in the leaves of Tradescantia and Bromeliacese ; in the stems and petioles of Dicotyle- 

 dons it commonly consists of collenchyma, the cells of which are extended longitudinajly, 

 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 Equisetaceae and leaves of Goniferae 

 (Fig. 102), or in long isolated fibres, similar to true bast-fibres, e.g. leaves of Cycadese. 

 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 



Fig. ioi. — Transverse section through the undergroiina bicui of 

 Pteris aquilina; 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. 



^ Since the pivblication of the 3rd edition of this work, a close investigation of the fundamental 

 tissue has been undertaken by Russow (/. c.) ; he has however occupied himself chiefly with the 

 various forms of the bundle-sheaths or ' Critenchyma.' 



