SACS CONTAINING RESINS AND GUM-RESINS. jaK 



T^iffering from the cells of the surrounding parenchyma in their more rapid growth, 

 and in the absence of any formation of even transitory chlorophyll or starch. It is 

 plain that the cases of subsequent swelling of sacs are to a certain extent connected 

 with those of secondary disorganisation. On the other hand, it cannot be denied 

 that these structures are closely related to mucilaginous epidermal cells (p. 73), and 

 sacs containing raphides (p. 139), and to sclerenchymatous elements, e.g. those of 

 the bark of Punica. 



3. Sacs containing resins and gum-resins. 



Sect. 34. Sacs, which from the moment of differentiation of tissues are per- 

 manently filled with the above-named bodies, the resin being usually accompanied 

 by ethereal oil, occur as characteristic components of numerous families, or of single 

 genera and species ; in the latter case they usually represent at certain places the 

 intercellular reservoirs, which occur in other parts of the same plant (e. g. Tagetes, 

 Lysiraachia), comp. Sect. 50. 



Taking the extreme cases into account, we may distinguish two forms of these 

 sacs, short and long. The former are of almost iso-diametric and usually roundish 

 foijtn, and have thin, smooth, homogeneous membranes which, in the cases hitherto 

 investigated (Laurus, Camphora, Acorus Calamus, Zingiberacese, Canella), give when 

 mature a yellow instead of a blue coloration with iodine and sulphuric acid, and 

 are not destroyed by strong action of the acid ^ Protoplasm is apparently absent in 

 the mature sac, which is completely filled by one homogeneous variously-coloured 

 di-op .of resin, or by an aggregation of several of these. Sacs of this category lie 

 solitary, or in small groups in the parenchyma (primary or secondary), with the cells 

 of which they are strongly contrasted by their highly refractive contents, and are 

 often distinguished by their more considerable size, in the Ziiigiberacese, Acorus, 

 Piperacese, Lauracese^ Magnoliacese (Magnolia, Drimys, Liriodendron',) Canellacese, 

 ■in the cortex of Croton Eleuteria, and its allies (Cascarflla bark), Galipea officinalis 

 (cortex Angusturse *), and Aristolochiaceae. In the majority of the above groups 

 and genera the sacs in question are the only reservoirs of the characteristic secre- 

 tions. But Galipea has also, according to the statements of Engler °, intercellular 

 reservoirs in the primary parenchyma. 



In the root of Acorus ' Calamus and gramineus, the inner of the two superficial 

 .layers is composed of regular prismatic resin-sacs. Van Tieghem ascribes a similar 

 structure to the roots of Xanthochymus pictorius, and Rheedia lateriflora, in which 

 the intercellular reservoirs present in the stem and leaf are absent, and are replaced 

 by these sacs (comp. below. Sect. 50). It remains to be investigated whether the 

 •hypodermal'layer of tissue containing drops of oil and resin, which is described in 

 the roots of Valeriana, belongs to this category '. 



' [Compare Zacharias, Bot. Zeitg. 1879, p. 617.] 



' Unger, Anatomie und Physiol, p. 210. ^ Treviranus, Beitrage, figs, 34, 35. 



* Compare the figures in Berg's Atlas z. Pharm. Waarenkunde, which refer to the above-named 

 barks and other drugs produced from the families above cited. 

 ' Studien iiber d. Rutaceen, &c., Halle, 1874. 



" Van Tieghem, Struct. de= Aroidees, Ann. Sci. Nat. 5 ser. torn. VI. p. 175. 

 ' Compare Meyen, Secretionsorgane, p. 63, Taf. VI. fig. 22. 



