148 SECRETORY RESERVOIRS. 



and with the less common lateral surfaces of contact of sacs which ai-e contiguous 



longitudinally. 



The rows of sacs are continued into the foliage leaves: they have here a similar 

 position and structure to those in the scales of the bulb, but the sacs are much more 

 elongated, and the fluid contents less cloudy. Similar sacs to those of Allium have 

 hitherto been found only in species of Triteleia (Hanstein). 



2 . The ' Sap cavities ' in the leaves of officinal and other species of Aloe are of doubtful 

 relationship to the structures under discussion. They accompany the longitudinal vascu- 

 lar bundles in the form of a band of prismatic sacs, which presents in transverse section 

 a semicircular multiseriate appearance : these sacs have flat ends and are arranged one 

 above another in longitudinal rows. The length of one sac varies, according to Trlcul's 

 measurements, e.g. in A. vulgaris, from 0-40™'" to 1-30""°, while the width is consider- 

 able, being, in the species above named, as great as o'lo — o-i3™°i. They are thin-walled, 

 and are filled, according to the species, locality, and time of year, with 'sap' of varying 

 intensity of colour, or even with colourless 'sap' (Aloe arborescens, plicatilis), which is 

 homogeneous, or it contains suspended in it spherical drops, which vary in number, size, 

 and special structure. It has been asserted that by disorganisation of single sacs, cavities 

 are formed in the band, which contain the same ' sap.' It is not improbable that the 

 gum-resin, which is the ' Aloe ' of the shops, is derived from these sacs, but even this is 

 not certain. The band is marked off from the surrounding chlorophyll-parenchyma by 

 a layer of apparently prismatic, rather flattened small cells or sacs, which often also con- 

 tain coloured sap, and in these Fliickiger saw, in A. soccotrina, after slow evaporation of 

 the ' clear, tenacious, beautiful yellow contents,' distinct yellovif plates (of Aloin ?) crys- 

 tallise out. For further details about these organs, which still require exact investigation, 

 see Unger, Anat. u. Physiol, p. 206 ; Fluckiger, Pharmacognosie, p. 106, and the detailed 

 account of Trecu), Compt. rendus, i Mai, 187 1 ; Ann. Sc. Nat. 5 serie, t. XIV. p. 80. 



Numerous species of Haworthia and Aloe ciliaris have, according to Trecul, no 

 secretory sacs. 



3. In j^e stems of Sambueus (S. nigra, S. Ebulus) there occur in the cortex outside the 

 vascular bundles, and especially in the periphery of the pith, longitudinal lines, which turn 

 dark brown on drying, and in this condition have even been regarded as Fungi '. Accord- 

 ing to Dippel's exposition'*, which I find to be confirmed in all essential points, these lines 

 consist of elongated, spindle-shaped sacs of very considerable length and breadth, which 

 are tapered at both ends. The transverse section of these sacs is round, and the breadth 

 varies between 0-025 ™™ and o'i64™'» (Dippel). It is stated by Dippel that the 

 length of the mature sac usually exceeds 18 — 20 mm; the only one isolated by him 

 without injury was 14™™ in length. They seem to me to reach a considerably higher 

 figure, and even to equal the whole length of an internode, that is to attain a length of 

 20"™ and more: but it is difficult to decide this for certain, owing to the difficulty of 

 isolating them intact. At all events these lines consisting of sacs, which turn brown on 

 drying, traverse the whole length of the internodes, and even pass through the nodes 

 from one internode into the next. The membrane of the sacs is rather thin and 

 colourless: in older internodes it is thickened and stratified, and has round or oval, 

 non-perforated pits. The contents are, when young, a cloudy, finely granular, rather 

 tenacious mass, which fills the whole cavity. In older stages this mass is often attached, 



■ partially or entirely, to the walls, and the central cavity is then filled with an apparently 

 watery fluid : in old parts it assumes an homogeneous, firmly gelatinous character, and 



' Compare Oudemans, Over eene bijzondere soort von buizen in den Vlierstam (Sambueus nigra), 

 tot hiertoe voor een fungus (Rhizomorpha parallela Roberge) gehouden. Verslag. k. Acad, von 

 Wetenschappen, Natuurkunde, 2 Reihe, torn. VI. (1872). 



^ Die milchsaftfiihrenden Zellen der Holunderarten. Verhandl. d. Nat. Vereins f. Rheinland 

 u. Westphalen, Jahrg. 32, pp. 1-9, Taf. I (1866). 



