the Vasa propria, and Receptacles of the Juices of Plants. 343 



if we find in all plants a system of vessels of the like kind, oc- 

 cupied by liquids differing only by being either limpid or else 

 coloured, then functions of a general importance must be attri- 

 buted to this vascular system, and both forms must be regarded 

 as canals permeated by the descending sap or the nutritive 

 juice. 



The numerous observations we have made place it beyond 

 doubt that, in the generality of non-lactescent plants, tubes are 

 to be found filled with an elaborated liquid, in which granules 

 are frequently to be seen in great abundance and of variable 

 magnitude. I have found such in almost every plant in which 

 I have sought them ; for example, their presence may be descried 

 with great facility in the Cucurbitacese, the thin transparent 

 tissues of which are of large size. If a vertical slice of a fibro- 

 vascular bundle be removed from Pepo after the plant has been 

 boiled, the cortical portion of these bundles may be seen to be 

 almost entirely formed by tubes filled with a liquid holding 

 numerous granules in suspension. These granules are small, 

 unequal, ill-defined in form, and sometimes of a greenish hue. 



But these liquids essentially differ from the coloured juices. 

 The latter contain caoutchouc, fatty matters, organic principles 

 possessing properties often of singular energy, and which stand 

 in no sort of relation to the organs with which they are 

 associated; moreover they do not turn blue under the action 

 of iodine. The juices of the straight tubes are simple in com- 

 position. M. Trecul has shown (Institut, No. 1487, p. 215) 

 that the granules of the cortical fibres become blue when per- 

 meated by an aqueous solution of iodine ; they therefore contain 

 starch — a principle isomeric with cellulose, the base of all the 

 tissues. 



In relation to physical properties, the juices compared to- 

 gether are not less distinct : the one sort is coloured, as already 

 stated, and the other limpid ; and although the fluids of the 

 latter description may contain granules, the appearances they 

 present when extravasated differ from those exhibited by the 

 ' former. The difference is particularly striking when the milky 

 and the limpid juices of the bark are examined in a plant in 

 which they are readily separated — for example, in the Acer 

 canipestre. If a drop of the milky juice be placed on a glass 

 slide, it is seen that, as it dries up, it becomes progressively 

 capable of being di-awn out into very long elastic threads : 

 when dried, it has the appearance of a uniform semitransparent 

 mass, in which the granules cannot be detected, and which 

 remains completely undivided and homogeneous. But if a drop 

 of the limpid fluid be placed on the glass, it rapidly dries and 

 breaks up in the fashion of gummy substances. The meshes 



