STONE-ELEMENTS. j^y 



Sect. 29. The term Short selerenoliymatous elements may be applied to 

 all forms which have not pointed tapering ends ; these are sometimes iso-diametric, 

 sometimes moderately elongated. To this group belong — 



(3) The sione-elemenls (' stone-cells ' of the Pharmacologists), so called after the 

 stony bodies in the flesh and stalk of many pears, which are composed of them, 

 are almost iso-diametric, rarely rod-like elongated derivatives of cells (' rod-cells '), 

 with stratified, very strongly thickened membrane, lignified to a stony hardness: 

 this wall is perforated frequently by numerous, usually branched pit-canals, of circular 

 appearance in transverse section (Fig. 52). The narrow internal cavity, which usually 

 disappears, is occupied by a watery fluid with a few granules, 

 or often by a reddish brown, apparently formless mass. 

 Stone-elements of this sort are widely spread among the 

 Dicotyledons, especially in sappy, fleshy parts ; in the suc- 

 culent parenchyma they are sometimes isolated, but usually 

 in uninterrupted connection with one another, forming cir- 

 cumscribed groups, or masses, of which the elements bor- 

 dering on the thin-walled tissue may graduate into the latter 

 by the thickening of their walls at this limit being one-sided 



i 1 T.i 11 3.^ 1,1 1 FIG. 52.— Transverse section of 



and weaker. In the so-called stout succulent plants, how- a short scierenchymatous (stone) 



, ,. ^^ , r~^ ^ - . element from the root tuber of 



ever, sucti as trie Crassulaceae, Cactacese, &c., stony formations Dauia variabilis, /lumen. *pit- 



11 ,. T-i ■ ., 1 1. 1 t canals; J"/ split, by which an inner 



are generally wanting. Jixquisite examples are supplied by systemofiayersisseparated^oj). 

 the fleshy body of Helosidese, Lophophytum, LingsdorSia', 



fleshy tuberous roots, e.g. Pseonia, Dahlia (Sachs) ; Rhizomes, e. g. Dentaria pinnata, 

 the pith of Hoya carnosa ", Medinilla spec.,' and especially the cortex of ligneous 

 Dicotyledons, in which they are mainly derived from secondary sclerosis of parenchy- 

 matous cells, as will be more closely described in Chap. XV. 



Transitional forms to the sclerenchymatous fibres are supplied by the rod- 

 shaped stone-elements of many cortical layers, the short pointed fibres of the 

 Cinchoneae, the short and pointed branched stone-elements of the cortex of Firs 

 and Larches, &c. 



In the Monocotyledons the elements of this category are rare ; but we must 

 include under this head the multiseriate dense layers beneath the epidermis of stems 

 of Palms *, and elements with large cavity, and large pits, which form in the cortex 

 of the root of many Aroids (e. g. Tornelia fragrans) 3-4 layers of cells outside the 

 endodefmal sheath of the vascular bundle, and in Raphidophora angustifolia ° also in 

 the inner cortex of the stem a ring of 1-2 layers in thickness. 



Typical stone-elements are wanting in the Cryptogams. 



(i5) A second form of short sclerenchyma is represented by the peculiar covering 

 plates which Mettenius" first distinguished in species ofTrichomanes under the name 



' Hooker, Trans. Linn. Soc. vol. XXII.— Graf Solms-Laubacli, in Pringsheim's Jahrb. VI. p. 

 530. — Eichler, Balanophores Brasilienses, Tab. II. 



^ Mohl, Ranken- und Schling-pflanzen, p. 89.— Ibid. Poren d. Pflanzenzellgewebes, p. 32. 



' A. Gris, Ann. Sci. Nat. 5 ser. XIV. p. 50. 



' Mohl, Palmarum structiira, pag. VI. Tab. A. C. Verm. Schrifteu, p. 136. — Botan. Zeitg. 

 1871, Taf. II. 



' Van Tieghem, Struct, des Aroidees, I.e. ' Hymenophylleen, I.e. p. 418. 



