]53 SECRETORY RESERVOIRS. 



strings. But careful investigation and comparison of corresponding transverse sections 

 shows that they never appear in the same radial planes (or only in rare cases, and then 

 only few of them), but in the large majority of cases in different planes. 



As the laticiferous sacs of the bast-ring draw nearer to the outer cortex, they lose the 

 milky nature of their contents: they appear constantly more watery, while the sacs them- 

 selves become gradually more and more compressed, and finally unrecognisable. 



The above relations of distribution and arrangement of the laticiferous reservoirs hold 

 also for the petiole. In the lamina laticiferous sacs appear as elements or concomitants 

 of the nerves, or are found here and there solitary in the parenchyma, in which case 

 they are always characterised there by considerable size. 

 . The membrane of the single laticiferous sacs, whether in the outer or inner cortex, the 

 pith, or the leaf, appears in the large majority of cases of equal thickness throughout. 

 It is as a rule very thin, and equal to that of the neighbouring cells of the parenchyma, or 

 even thinner. However I recognised in many sacs of the inner cortex partial thickenings 

 of the walls : these appear distributed at many points : they appeared swollen, and a slight 

 protuberance of the outer surface of the cell usually corresponded to such points. — The 

 membranes of the laticiferous sacs are colourless ; they give a blue reaction with Schultze's 

 . solution, but usually the colour is fainter and less pure than that of the surrounding 

 parenchyma. 



The contents of the laticiferous sacs have sometimes the character of an emulsion, and 



accordingly appear white by reflected light, showing under the microscope as a finely 



. granular dark mass — this is always the case in the reservoirs of the inner cortex; 



sometimes they form more or less refractive plugs resembling homogeneous masses of 



- resin : these are usually colourless, or light yellow, and fill the cavity of the sac com- 

 pletely. These plugs can easily be isolated from sections under water, when their be- 

 haviour under solvents can be investigated. They occur chiefly in the outer cortex. 

 Carbon disulphide, chloroform, and benzol dissolve the mass almost completely: ether 



..leaves a considerable granular residue. Alcoholic solution of iodine colours it golden 

 yellow. Addition of alcohol removes the resinous appearance, and makes the mass itself 

 dark and finely granular. If freshly isolated pieces of latex be exposed to concentrated 



. sulphuric acid, they are dissolved gradually with a yellow colour : dilute sulphuric acid 

 first produces swelling, while homogeneous drops escape from the substance, the outline of 

 which soon becomes indistinct ; their substance then gradually dissolves in the surround- 



- ing fluid, and colours it yellow. Meanwhile the original contour of the string of latex is 

 retained : it appears that one substance is extracted while the other remains undissolved. 

 The latter was in many cases found still undissolved after long immersion (two days) in 

 sulphuric acid. Potash produced no apparent change. 



In many laticiferous sacs of the outer cortex dusky-looking contents may be found, con- 

 sisting of numerous drops of the most variable size : they dissolve immediately in water. 

 One is tempted to assume that the before-mentioned resinous contents develop gradually 

 from this latex, which is easily soluble— they occur however in the highest regions of the 

 stem immediately below the punctum •vegetationis — nevertheless this phenomenon de- 

 serves attention, viz. that the resinous plugs in the outer cortex assume, after treatment 

 with alcohol, an appearance which coincides remarkably with that of the contents of the 

 inner cortex. The latter may be completely dissolved by warming with dilute potash : 

 when treated less strongly with this reagent there are sometimes formed from it 

 numerous small crystals or isolated large ones, which disappear quickly on adding acetic 

 acid. , 



The laticiferous reservoirs of the pith were not accurately investigated as regarded 

 their contents, which coincided exactly in optical properties with that of the sacs in the 

 outer cortex ^. 



' [On Resin-sacs in Hypericxim, compare v. Hbhnel, Bot. Ztg. 1882, 149.] 



