I04 



MORPHOLOGY OF TISSUES, 



japonica, the erect post-like cells upon which the stomata of the leaves of Hakea are, as it 

 were, supported). All these tissue-formations are enveloped by the epidermis, and fre- 

 quently also by hypodermal tissues. In the carpellary leaves of Phanerogams there oc- 

 curs commonly a more manifold differentiation of the fundamental tissue ; I will instance 



only the formation of the so- 

 called stones of Drupaceae. The 

 stone is here the inner layer of 

 tissue of the same foliar struc- 

 ture of which the outer layers 

 form the succulent flesh of the 

 fruit ; both are the fundamental 

 tissue of the carpel, the former 

 sclerenchymatous, the latter pa- 

 renchymatous and succulent, both 

 being traversed by fibro-vascular 

 bundles. Equally clear is the 

 structure in the stems of Ferns, 

 among which the Tree-ferns and 

 Pteris aquUina are of special in- 

 terest, because the fundamental 

 tissue occurs in them in two 

 quite different forms ; its pre- 

 ponderating mass consists, e, g. 

 in Pteris aquiUna (Fig. 80) of a 

 thin -walled colourless mucila- 

 ginously succulent parenchyma, 

 in winter rich in starch, in 

 which there also run, parallel 

 with the fibro-vascular bundles, 

 filiform or strap - shaped lines 

 of thick - walled prosenchyma- 

 tous dark brown bundles of 

 sclerenchyma. They have no- 

 thing in common with the fibro- 

 vascular bundles, but are only a 

 peculiar form of the fundamental 

 tissue which also often occurs 

 elsewhere in Cryptogams in pro- 

 senchymatous forms. The ten- 

 dency to prosenchymatous de- 

 velopment of the cells of the 

 fundamental tissue occurs also 

 especially in the stems of Lyco- 

 podiacese. In Selaginella denti- 

 culata (Fig. 87, y^) the axial fibro- 

 vascular bundle is surrounded 

 by a very loose parenchyma 

 which forms large intercellular 

 spaces ; this innermost portion of the fundamental tissue is enveloped by a thin- 

 walled tissue without interstices, which shows itself on longitudinal section to be deve- 

 loped prosenchymatously ; the cells are pointed above and below, and penetrate to a 

 considerable distance between one another; towards the circumference 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 



Fig. Z-j.—A transverse section of the stem oi Selaginella dentictdata; the 

 fibro-vascular bundle is not yet fully developed ; the vessels are already lignified 

 on both sides, but not yet in the centre; / air-conducting intercellular spaces 

 in the parenchyma enveloping- the bundle ; towards b the part of the tissue 

 corresponding to the bundle which bends outwards to the leaf. R transverse 

 section of the mature stem of LycopodiH??t cha7nc?cyparisstis, the axial tissue- 

 cylinder consists of densely crowded and coalescent fibro-vascular bundles ; the 

 four parts of their xylem are quite separated, forming four bands on the trans- 

 verse section, between and around which are found the narrower cells of the 

 phloem. The phloem portions of the four bundles have coalesced ; between each 

 pair of xylem-bundles is seen a row of wider cells, the latticed cells or sieve- 

 tubes ; the narrow cells lying on the right and left edge of each xylem portion 

 are spiral-vessel-cells (also in A). In the thick-walled prosenchymatous funda- 

 mental tissue which envelopes the axial cylinder, is seen the dark transverse 

 section, of a thin fibro-vascular bundle which bends outwards to a leaf; it con- 

 sists almost exclusively of long spiral-vessel-cells (X about 90). 



