SACS CONTAINING RESINS AND GUM-RESINS. 



i47 



elements in the parenchyma of the secondary wood of Cotiiferse belong to this series. 

 (Comp. Chap. XIV.) 



As doubtful cases may here be mentioned the sacs filled with pigment, in 

 Sanguinaria, Glaucium, and Macleya, which will be again noticed in Sect. 47 ; the 

 sacs or cells containing gum-resin which accompany the vascular bundles of species 

 oi Aloe; lastly, the various 'cells' filled with peculiar pigments (usually watery 

 solutions), such as those in the roots of Rheum ^, Rubia, &c. 



The following particulars may be quoted concerning those organs of this 

 series which have been more accurately investigated. 



I. Hanstein''' discovered in those species of Allium in which he sought them (A. Cepa, 

 fistulosum, ascalonicum, &c.), large wide sacs, which he grouped with the series of 

 raphide-containing s^s of other Monocotyledons, as sac-like vessels (vesicular vessels). 

 As regards their form and arrangement they closely resemble these latter sacs, e. g. those 

 of the Amaryllidacese, though they differ from them in structure, and especially in the 

 character of their contents. 



In the scales of the bulb of species of Leek they appear as numerous opaque lines, 

 which are visible to the naked eye, and run longi- 

 tudinally like nerves. They lie near the outer 

 surface of the scale, between the second and third 

 layers of parenchyma. The single sacs are of 

 circular transverse section, and wider than the 

 cells of the neighbouring parenchyma which abut 

 closely upon them ; they are much longer than 

 broad; are often somewhat swollen below their 

 flattened ends, and are arranged in longitudinal 

 series one above another (Fig. 56). 



At the base of the scale they are often shorter 

 than above, and not unfrequently bear sac-like 

 branches, which connect neighbouring series with 

 one another as transverse or oblique anastomoses: 

 here also rows of sacs occur in close longitudinal 

 aggregation. 



The sacs are filled with a granular cloudy fluid, 

 which appears to the naked eye on the surface of 

 sliced onions as a pale milk, in the sac itself it is 

 cloudy, but still transparent. The nature of the 

 constituents -of these contents has not yet been 

 thoroughly investigated : I have not been able 

 to substantiate the obvious conjecture that they 

 especially contain the oil of garlic. Raphides or 

 other crystals are entirely absent. A large, 

 slightly elongated nucleus is still to be found in 

 sacs that are not too old. The walls of the 

 . sacs are colourless and delicate, so that in sec- 

 tioiis they are squeezed in laterally by the turgescent parenchymatous cells : where 

 they touch the latter they are smooth or have solitary small round pits: but oyer 

 the whole surface where two sacs are in contact with one another the wall is, like 

 a coarse Sieve, covered with crowded, round— not perforated— pits, while between these 

 lie rather thick bands of membrane. This is the case both with the transverse walls. 



FiG.s6.—AlliuinCepa; longitudinal section through 

 a bulb-scale, e epidennis. c cuticle, / parenchyma ; 

 between the first and second layers of parenchyma 

 ends of two sacs which abut on one another and are 

 divided by the pitted transverse wall g—q ; they are 

 represented as cut in half longitudinally ; j^ their con- 

 tents coagulated by potash; the longitudinal wall 

 behind this abuts on another lower sac, and shows 

 accordingly the pitting mentioned in the text. From 

 Sachs' Textbook. 



* Unger, Anat. p. 3o6, 



"^ L.C., compare p. 139 



