SACS CONTAINING MUCILAGE. 



143 



foliage of Vitis, Cissus, and Ampelopsis : in Vitis they are found in the wood also, and, 

 together with klinorhombic crystals, in the bast, in the cortex of Clnnamonium Zeylani- 

 cum, and Olea Europea : in the foliage (leaves and stems) of species of Impatiens, Me- 

 sembryanthemum, and Phytolacca, in Nyctagineae, and QEnothereae. 



It will be seen from what is above stated that here also differences occur in equivalent 

 parts of plants closely allied to one another and of similar habit, and that one cannot 

 designate any form of crystal-containing sacs as a general peculiarity of a family, or as a 

 phenomenon of adaptation. Among the often-quoted Solanaceae the majority (e.g. 

 Solanum tuberosum. Dulcamara, species of Nicotiana, Scopolia atropoides, Jochroma 

 Warczewiczii) have very numerous sacs with granules throughout the parenchyma of 

 the stem (in the leaves often clustered crystals). Jochroma coccineum has granule- 

 containing sacs in large quantity in the parenchyma of the pith, but in the cortex only 

 solitary prismatic crystals : in Atropa Belladonna the granule-containing sacs are entirely 

 wanting in the foliage : it has been above noted that crystal-containing sacs are com- 

 pletely absent in Petunia. All these statements hold for true crystal-containing sacs, 

 and it must always be borne in mind that, besides these, smaller solitary crystals of all 

 forms may occur in the contents or in the membranes of other tissue-Qlements. 



The crystal-containing sacs appear while the tissues are still young, usually 

 when the tissues begin to differentiate ^ ; in the leaf of Citrus, according to Pfitzer, 

 their formation begins when it is about 3 ctm. in length : they are developed in 

 greater quantity only in the almost fully unfolded, but still tender leaf, when its cells 

 attain their last definitive extension and thickening of the membranes. They retain 

 unaltered through life that size and structure which they have attained when the 

 differentiation of tissues is complete. 



In connection with the crystal-containing sacs must be mentioned the occurrence 

 of cells containing Cystoliths, which are found in the Acanthaceas, and many Urti- 

 cacese (Pilea), in the epidermis of which they have been described above (p. 105), 

 also scattered in the parenchyma of the cortex, and even of the piih. As regards 

 their structure, all that has above been said of the same structures in the epidermis 

 holds good. 



2. Sacs containing mucilage. 



Sect. 33. When vegetable mucilage and gummy bodies, occurring within the 

 tissues, do not belong to the cell contents of assimilating parenchymatous cells (as is 

 the case with the plentiful mucilage in roots of Borraginaceae, e. g. Symphytum, 

 Cynoglossum, &c., or that of mucilaginous sappy parenchyma, e. g. in species of 

 Alocj comp. p. 116), they fill completely or almost entirely the cavity of special 

 mucilage-containing sacs ^. Such sacs occur in the parenchyma of the Malvaceae, 

 Tiliaceae, Sterculiaceae, in the cortex of the officinal Lauraceae, the Ulmeae, the Cac- 

 tacese^, and of the tubers of Orchis, also in the cortex of the firs (Abies pectinata 

 and its allies). They are in all cases distinguished from the cells of the surrounding 

 parenchyma by their greater size, and are distributed between these either singly, or 



^ Compare Hilgers, /. c. 



'^ Trecul, I'lnstitut, 1862, p. 314. — A. B. Frank, Ueber die Anatom. Bedeutimg, &c., ve^etab. 

 Schleime ; Priiigsheim's Jahrb. V, p. 161, Taf, XV, XVI. — Idem, Zur Kenntniss d. Pflanzenschleime, 

 Journ. f. pract. Chemie, Bd. 95. 



^ Schleiden, Anatomie d. Cacteen, p. 8, where, by the way, the structure is not rightly re- 

 presented. 



